TaxesCalculations

Methodology & Accuracy

Last reviewed: September 26, 2026

Every calculator on TaxesCalculations.com is powered by a small, tested calculation engine. This page documents the formulas, the tax-year data we maintain, and — just as importantly — the boundaries of what these tools model, so you can judge how far to trust a number.

It is also the reference behind the site's four guides, which walk the same engine through everyday questions: How Tax Brackets Actually Work (marginal versus effective rates, and why a raise into a new bracket cannot lower take-home pay), the 2026 Federal Tax Brackets tables for every filing status, What OBBBA Changes on Your 2026 Return, and Self-Employment Tax, Explained. The full list is on the guides page. Each guide states what it assumes; this page states what the engine does, calculator by calculator, with the inputs each one accepts and one worked example per tool computed at build time from the data described below.

One data file per tax year

All year-dependent constants — bracket thresholds, standard deductions, the Social Security wage base, Medicare thresholds, and the supplemental withholding rate — live in a single versioned data file, keyed by tax year. The calculators currently support:

  • 2026: standard deduction $16,100 (single) / $32,200 (married filing jointly) / $24,150 (head of household); Social Security wage base $184,500; 7 brackets from 10% to 37%.
  • 2025: standard deduction $15,750 (single) / $31,500 (married filing jointly) / $23,625 (head of household); Social Security wage base $176,100; 7 brackets from 10% to 37%.

When the IRS publishes the next year's inflation adjustments (typically each fall), that file gains an entry and every calculator updates together. Figures follow the IRS revenue procedures and SSA announcements listed under Sources below; confirm consequential numbers against IRS.gov.

A second data file for the OBBBA deductions

The five deductions introduced or rewritten by the One Big Beautiful Bill Act for tax year 2026 — the senior deduction, the SALT cap, car-loan interest, the standard-deduction detail, and the charitable rules — keep their constants in a separate file, because their figures are statutory rather than inflation-indexed and because each one needs its own citation. Every constant there is stored together with the primary source that justifies it; the senior deduction's amount, for instance, carries the citation "IRC §151(d)(5)(C), added by P.L. 119-21 §70103 (139 Stat. 159–160, govinfo.gov PLAW-119publ21); IRS newsroom OBBBA deductions page". The file records the date its figures were last checked against the enacted statute, the Internal Revenue Code, and the IRS revenue procedure — currently 2026-08-18. That check is absence-of-evidence: it means no later amendment had been found as of that date, not that the figures are final.

Three cross-cutting rules from that file govern how the OBBBA tools behave. The senior, car-loan, and charitable non-itemizer deductions are claimed on Schedule 1-A and flow to Form 1040 line 13b — they are subtracted after AGI, so they never reduce AGI or MAGI and are available whether or not you itemize. The MAGI their phase-outs consume is a uniform definition: AGI plus amounts excluded under IRC §§ 911, 931, and 933 — for most people, MAGI equals AGI. And the 2026 standard deduction figures already include OBBBA's permanent increase, so no calculator layers a separate bump on top; the OBBBA file's base amounts are asserted at build time to equal the tax-year file's, and the build fails if they ever disagree.

The core computations

The rates and thresholds quoted in this summary are read from the 2026 entry of the data files; each supported year carries its own, and the per-calculator sections further down show the same figures at work.

  • Bracket math: tax is accumulated slice by slice — each bracket rate applies only to the taxable income falling between its bounds. The marginal rate is the last bracket reached; the effective rate divides total tax by income.
  • Take-home pay: taxable income = gross − pre-tax retirement − standard deduction (floored at zero); federal tax via the brackets; Social Security at 6.2% of gross up to the wage base; Medicare at 1.45% of all gross plus the 0.9% surtax above the withholding threshold. Pre-tax 401(k) contributions reduce income tax but not FICA wages, matching actual payroll treatment.
  • Self-employment tax: 92.35% of net earnings forms the base; Social Security at 12.4% up to the wage base and Medicare at 2.9% (plus the 0.9% surtax above the threshold); the deductible half is half of the Social Security + 2.9% Medicare portions (the surtax is not deductible).
  • Bonus withholding: the percentage method — a flat supplemental rate up to $1,000,000 of supplemental wages and the top rate above, plus FICA with the wage base credited for year-to-date wages.
  • Sales tax: forward, tax = price × rate; backward, pre-tax = total ÷ (1 + rate) — division, not subtraction, which is the common manual error.
  • Quarterly estimated taxes: current-year tax is the bracket engine plus the self-employment engine (with the ½ SE-tax deduction applied to AGI); the required annual payment is the lesser of 90% of that or 100% of prior-year tax (110% when prior-year AGI exceeds $150,000), minus withholding, in four equal installments on the year's published due dates. Safe-harbor rules and dates verified against IRS Pub. 505 and Form 1040-ES; the Form 2210 penalty and the annualized-installment method are not computed.
  • Modified AGI (MAGI): purpose-specific — each definition applies only the add-backs its controlling worksheet lists: Pub. 590-A Worksheets 1-1 and 2-1 (traditional and Roth IRA), the Form 8962 instructions Worksheet 1-1 (ACA premium tax credit), and SSA POMS HI 01101.010 (Medicare IRMAA). Eligibility thresholds and premium brackets are deliberately not computed.
  • No Tax on Tips & Overtime (OBBBA 2025): the § 224 tips deduction (capped at $25,000 per return) and the § 225 overtime deduction (capped at $12,500 single / $25,000 joint) — for tax years 2025–2028. Only the FLSA overtime premium (rate above the regular rate) qualifies; each deduction phases out by $100 for every full thousand dollars of MAGI over $150,000 ($300,000 joint). Both are income-tax deductions only — FICA still applies — and the optional tax-saving figure is the bracket differential on a standard-deduction taxable-income proxy.

How to read a result

Every result is arithmetic on the numbers you entered, and the most common misreadings come from asking a result a question it was not built to answer. A marginal rate is the bracket of the last dollar — the price of one more dollar of taxable income — while an effective rate is total tax divided by income; the first is always at least as high as the second, and quoting one where the other belongs accounts for most bracket confusion. Withholding is not liability: the bonus tool computes what an employer withholds under the percentage method, which the annual return later reconciles against actual tax in either direction. A deduction is not a refund: the tips-and-overtime tool's estimated saving is the bracket differential on the deduction, not money returned, and every OBBBA deduction it and its siblings compute leaves Social Security and Medicare untouched. The senior, car-loan, and charitable non-itemizer deductions also leave AGI and MAGI untouched, so a result from one of those tools never changes the input to another; the tips-and-overtime tool's phase-out and saving estimate simply run on the MAGI you enter, which the engine never recomputes from the deduction. And the sales-tax tool applies whatever rate you supply — it has no table of jurisdictions and no opinion about which rate is correct. Results are planning estimates of the federal core; your actual liability is determined when you file.

What the calculators accept

Every money field runs through one shared parser before the engine sees it. It strips dollar signs, grouping commas, percent signs, and spaces, then accepts digits with an optional minus sign and decimal point, up to a magnitude of 1,000,000,000,000,000; anything else — "12a", "1.2.3", a blank — is reported on the field rather than silently coerced. The engine then applies its own rules and returns a typed error rather than a number when they fail, so no result can be built from an invalid input. Money inputs cannot be negative (a negative taxable income is refused with the message "The taxable income cannot be negative."); fields that make no sense at zero — annual income, net self-employment earnings, a bonus, a price, an hourly rate — must be greater than zero; and an upper ceiling of $1,000,000,000,000 keeps the floating-point arithmetic exact. Percentages have their own bounds, listed per tool below (a 95% retirement contribution, for example, is refused with "Enter a retirement contribution between 0% and 90%."). Filing status is single, married filing jointly, or head of household for the ordinary-income tools; married filing separately exists only where its own thresholds are meaningfully different — the capital-gains engine and the five OBBBA deduction tools (senior, SALT, car-loan, standard-deduction, and charitable) — and the standard-deduction tool additionally models a qualifying surviving spouse. The supported tax years are 2025 and 2026. The OBBBA MAGI fields are the one place a negative value is accepted, because AGI can be negative and a negative MAGI simply means no phase-out excess.

Calculator by calculator

Each subsection names the engine function the tool page calls, the inputs it takes and the ranges it enforces, and one worked example — with its tax year and filing status stated — computed at build time by that same function.

Tax Bracket Calculator

The Tax Bracket Calculator subtracts the standard deduction for your filing status from gross income, then calls federalTax(taxableIncome, status, year). Inputs: gross income (zero or more), filing status, tax year. The output is the list of bracket slices actually filled, the marginal rate, and the effective rate on taxable income. Example, married filing jointly, 2026: gross income of $142,000 less the $32,200 standard deduction leaves $109,800 of taxable income. The slices sum to $13,580.00. The last dollar lands in the 22% bracket, which taxed only the $9,000 above $100,800 — the effective rate is 12.37% of taxable income and 9.56% of gross. Why the inputs matter: filing status changes every threshold, and the deduction step is why the same salary lands in a lower bracket than a naive reading of the tables suggests.

Federal Income Tax Calculator

The Federal Income Tax Calculator calls the same federalTax() function but takes taxable income directly — no deduction is subtracted, which is the tool to use when the after-deduction figure is already known. Inputs: taxable income (zero or more), filing status, tax year. Example, head of household, 2026: $58,000 of taxable income produces $6,606.00 of tax, a marginal rate of 12% and an effective rate of 11.39%. The common misreading is entering gross income here: the result then overstates tax by whatever the deduction would have removed from the top slices. The bracket-by-bracket lines in the output show exactly which slice each dollar of tax came from, so a surprising total can be traced rather than trusted.

Take-Home Pay Calculator

The Take-Home Pay Calculator calls takeHomePay(grossIncome, status, year, preTaxRetirementPct); its comparison mode runs the function twice and passes both results to compareTakeHome(a, b) and classifyComparison(). Inputs: gross annual income (greater than zero), filing status, tax year, and an optional pre-tax retirement contribution between 0% and 90% of gross. The contribution reduces taxable income but not FICA wages; Social Security applies at 6.2% up to the $184,500 wage base, Medicare at 1.45% of all wages, and the 0.9% surtax above $200,000. Example, single, 2026: $72,000 gross with a 6% contribution sets aside $4,320.00, leaves $51,580.00 taxable, and produces $6,059.60 of income tax, $4,464.00 of Social Security, and $1,044.00 of Medicare — annual take-home $56,112.40, or $4,676.03 a month and $2,158.17 per biweekly paycheck, with all federal taxes at 16.07% of gross. The comparison mode, given a raise to $78,000 with nothing else changed, reports take-home up $3,940.20 — a keep rate of 65.67% of the extra gross after federal income tax, FICA, and the 6% contribution on the new dollars. The keep-rate figure is shown only when salary is the sole difference; when filing status, year, or the contribution also moved, the delta is a combined effect and the tool says so instead.

Hourly to Salary Calculator

The Hourly to Salary Calculator calls hourlyToSalary(hourlyRate, hoursPerWeek, overtimeHoursPerWeek, overtimeMultiplier) and computes no tax at all — it annualizes gross pay over 52 weeks so the result can be carried into the take-home tool. Ranges: hourly rate greater than zero; weekly hours between 1 and 100; overtime hours between 0 and 80; overtime multiplier between 1 and 3 (the FLSA standard time-and-a-half is the default). Example, 2026, any filing status — the function takes neither a year nor a status: $32 an hour for 38 hours plus 4 overtime hours at 1.5× is $1,408.00 a week, of which $192.00 is overtime — $73,216 a year, $6,101.33 a month. Where it stops: the 52-week year assumes no unpaid weeks, and nothing here is after tax.

Bonus Tax Calculator

The Bonus Tax Calculator calls bonusWithholding(bonus, year, ytdWages). Inputs: the bonus (greater than zero), tax year, and year-to-date wages (zero or more, default zero). Federal withholding is the percentage method — 22% of supplemental wages up to $1,000,000 and 37% above; Social Security applies only to the part of the bonus still under the wage base once year-to-date wages are credited; Medicare applies to all of it, with the surtax when year-to-date wages plus the bonus cross the threshold. Example, 2026, any filing status — the percentage method does not use one: a $20,000 bonus paid when year-to-date wages are $176,500 — $8,000 short of the $184,500 wage base. Federal withholding is $4,400.00; Social Security is $496.00 rather than $1,240.00, because only $8,000 of the bonus is still under the base; Medicare is $290.00. Total withheld $5,186.00, net bonus $14,814.00. This is withholding, not final tax: the bonus is reconciled with everything else on the annual return, where the same dollars are taxed at your actual marginal rate.

Self-Employment Tax Calculator

The Self-Employment Tax Calculator calls selfEmploymentTax(netEarnings, year). Input: net self-employment earnings (greater than zero) and the tax year; no filing status is asked because the core computation does not depend on one. The base is 92.35% of net earnings; Social Security applies at 12.4% of the base up to the wage base and Medicare at 2.9% of all of it, with the surtax above the threshold — applied at the single-filer figure for every status. Example, 2026, any filing status: $64,000 of net earnings gives a base of $59,104.00, $7,328.90 of Social Security and $1,714.02 of Medicare — $9,042.91 in all, 14.13% of net earnings — and a deductible half of $4,521.46. The deductible half reduces taxable income for the income-tax computation only; it does not reduce the self-employment tax itself, and the surtax is excluded from it. Income tax on the same earnings is a separate computation, which is what the quarterly tool adds.

Quarterly Tax Calculator

The Quarterly Tax Calculator calls quarterlyEstimatedTax(expectedAgi, status, year, options), where the options are expected net self-employment earnings, expected withholding, and the prior year's total tax and AGI. Ranges: expected AGI (entered before the half-SE deduction, which the engine subtracts itself) and every option are zero or more; AGI and self-employment earnings cannot both be zero; and the two prior-year figures must be supplied together or not at all. The required annual payment is the lesser of 90% of the current year's estimated tax and 100% of prior-year tax — 110% when prior-year AGI was above $150,000. Payments are required only when the balance after withholding is at least $1,000 and withholding falls short of the required amount. Example, married filing jointly, 2026: expected AGI of $130,000 including $30,000 of self-employment profit, $9,500 of withholding, and prior-year tax of $14,200 on $118,000 of AGI. Self-employment tax is $4,238.87; its deductible half of $2,119.43 and the $32,200 standard deduction leave $95,680.57 taxable and $10,985.67 of income tax — $15,224.53 of current-year tax in scope. 90% of that is $13,702.08; 100% of prior-year tax is $14,200.00; the lesser, $13,702.08, is the required annual payment. After withholding, $4,202.08 remains — $1,050.52 per installment, due April 15, 2026, June 15, 2026, September 15, 2026, January 15, 2027. The due dates are per-year data, not a formula, because weekend and holiday shifts are published by the IRS each year. Not computed: the Form 2210 underpayment penalty and the annualized-income installment method.

MAGI Calculator

The MAGI Calculator calls modifiedAgi(purpose, inputs) with the purpose set to one of traditional-ira, roth-ira, aca-ptc, or irmaa. Inputs: AGI (zero or more) and only the add-back fields that purpose's controlling worksheet lists; fields irrelevant to the chosen purpose are ignored, and Roth conversion income — the one subtracted line — cannot exceed AGI. Example, ACA premium-credit purpose, 2026, any filing status — the add-back arithmetic takes neither a year nor a status: $52,000 of AGI plus $1,200 of tax-exempt interest and $9,000 of untaxed Social Security benefits is a MAGI of $62,200. The same three numbers under the Medicare IRMAA purpose give $53,200, because that definition adds only tax-exempt interest — which is the point of the tool: "modified AGI" is not one number. The output is the MAGI figure alone; the contribution limits, credit amounts, and premium brackets those figures feed are deliberately not computed. Note that the OBBBA tools use a different, uniform MAGI — AGI plus the §§ 911, 931, and 933 exclusions — described above.

Sales Tax Calculator

The Sales Tax Calculator calls salesTax(price, ratePct) to add tax and salesTaxReverse(total, ratePct) to extract it from a receipt total. Ranges: price or total greater than zero; rate between 0% and 50%. The tool carries no jurisdiction data — the rate is entirely yours. Example, 2026, any filing status — the computation uses neither — at an illustrative 8% (the tool has no jurisdiction table; supply your own rate): a $86.40 total divides to a $80.00 pre-tax price and $6.40 of tax. Subtracting 8% of the total instead gives $79.49, which is wrong because the rate was applied to the pre-tax price, not to the total — the division-versus-subtraction error the backward mode exists to prevent. Forward, $129.99 at an illustrative 6.5% is $8.45 of tax and a $138.44 total.

Capital Gains Tax Calculator

The Capital Gains Tax Calculator calls capitalGainsTax(taxableOrdinaryIncome, longTermGain, status, year, options), the one tax.ts function that models married filing separately (the OBBBA deduction tools in obbba.ts model it separately, as the inputs section notes). Inputs: taxable ordinary income and the net long-term gain (each zero or more), filing status, tax year, an NIIT toggle, and an optional MAGI for the NIIT test. The gain occupies the taxable-income interval from ordinary income up to ordinary income plus the gain, and each band taxes only the part of that interval it overlaps — for married filing jointly in 2026, 0% up to $98,900, 15% up to $613,700, 20% above. Example, married filing jointly, 2026: $90,000 of ordinary income and a $20,000 gain — $8,900 of the gain rides at 0% and $11,100 at 15%, $1,665.00 in all, an effective 8.33% on the gain. With NIIT on, the 3.8% tax applies to the lesser of the gain or the MAGI excess over the statutory threshold. Example, married filing separately, 2026: $110,000 ordinary, a $30,000 gain, MAGI $140,000 — band tax $4,500.00; the NIIT base is $15,000, the excess over the $125,000 threshold rather than the whole gain, for $570.00 more and $5,070.00 in total. Out of scope by design: short-term gains, state taxes, § 1250 recapture, collectibles, QSBS, and the § 121 home-sale exclusion.

Crypto Capital Gains Calculator

The Crypto Capital Gains Calculator uses the same capitalGainsTax() engine for a net long-term gain, and prices a short-term gain exactly as ordinary income: federalTax() on taxable income with the gain, minus federalTax() without it. The short-term check offers single, married filing jointly, and head of household only, because the ordinary bracket tables do not model married filing separately. Example, head of household, 2026: a $6,000 short-term gain on $54,000 of taxable income costs $720.00 — it fills the 12% bracket — while the same gain held more than a year costs $0.00, because the interval from $54,000 to $60,000 sits entirely inside the head of household 0% band, which ends at $66,200. Both modes start after the cost-basis work: bring the net gain, not the transaction history.

No Tax on Tips & Overtime Calculator

The No Tax on Tips & Overtime Calculator first calls qualifiedOvertimePremium(regularRate, overtimeHoursPerWeek, overtimeMultiplier) to isolate the FLSA premium, then noTaxTipsOvertime({ tipIncome, overtimePremium, status, year, magi }). Ranges: tips and premium zero or more but not both zero; overtime hours between 0 and 80 a week; multiplier between 1 and 3; MAGI optional and zero or more — when omitted, no phase-out is applied and no saving is estimated. Statuses are single, married filing jointly, and head of household; the statute excludes married filing separately. Tax years outside 2025–2028 return a zero deduction. Tips are capped at $25,000 per return; the overtime premium at $12,500 for single and head of household filers and $25,000 joint; each is reduced by $100 for every full thousand dollars of MAGI over $150,000 ($300,000 joint). Example, single, 2026: $4,000 of tips, and $28 an hour for 6 overtime hours a week at 1.5× — a premium of $4,368.00, the $14.00 above the regular rate each hour, never the full $42.00 overtime rate. A MAGI of $156,400 is $6,400 over the threshold — 6 full thousands, so $600 comes off each deduction: tips $3,400, overtime $3,768.00, $7,168.00 in total. The estimated income-tax saving is $1,720.32 at the 24% bracket — a deduction's bracket value, not a refund — and Social Security and Medicare are unchanged.

Senior Deduction Calculator

The Senior Deduction Calculator calls seniorDeduction({ status, taxpayer65, spouse65, magi, hasRequiredSsns }). Inputs: any of the four filing statuses, whether the taxpayer (and, on a joint return, the spouse) will be 65 by year end, and MAGI — which may be negative. Each qualified individual gets $6,000, reduced by 6% of the MAGI excess over $150,000 (joint) or $75,000 (all other statuses), applied per person; married filing separately is ineligible, and the deduction exists for tax years 2025–2028. Example, head of household, 2026: a filer aged 65 with a MAGI of $95,000 is $20,000 over the threshold, loses $1,200 to the phase-out, and deducts $4,800. The tool echoes the MAGI it consumed unchanged: this is a Schedule 1-A deduction, available whether or not you itemize, and it never reduces AGI or MAGI. It is also separate from the age-65 additional standard deduction, which the standard-deduction tool computes.

SALT Deduction Cap Calculator

The SALT Deduction Cap Calculator calls saltCap({ status, magi, saltPaid }). Inputs: filing status, MAGI (may be negative), and the state and local taxes paid (zero or more). For 2026 the cap starts at $40,400 and falls by 30% of the MAGI excess over $505,000, but never below $10,000; for married filing separately the engine phases down, applies the floor, and only then halves — a $20,200 starting cap, a $252,500 threshold, and an effective floor of $5,000. The allowed deduction is the lesser of what you paid and the applicable cap. Example, single, 2026: a MAGI of $530,000 is $25,000 over the threshold, which takes $7,500 off the cap, to $32,900; with $38,000 paid, $32,900 is deductible and $5,100 is lost to the cap. This is an itemized deduction, so it matters only when itemizing beats the standard deduction — the tool page links to the standard-deduction calculator so you can compare. Later years are described qualitatively only, in the data file's own words: "The cap and threshold rise about 1% per year through 2029; exact 2028–2029 dollar amounts have no statutory rounding rule — awaiting IRS guidance."

Car Loan Interest Deduction Calculator

The Car Loan Interest Deduction Calculator calls autoLoanInterestDeduction({ status, magi, interestPaid, eligibility }), where eligibility is a yes-or-no answer to each of the 7 statutory gates (New vehicle; Personal use; Qualified vehicle type; Final assembly in the U.S.; Qualified loan; No exclusions apply; VIN reported on the return) — all must pass. Inputs: filing status, MAGI (may be negative), and the interest paid (zero or more). Interest is capped at $10,000 first; the result is then reduced by $200 for each $1,000 or portion thereof of MAGI over $100,000 (single, head of household, and married filing separately) or $200,000 (joint). Because a partial increment counts in full, the phase-out is a staircase, and the deduction is gone for any MAGI above $149,000 or $249,000 respectively. Example, head of household, 2026, all gates passed: a MAGI of $103,400 is $3,400 over the threshold — 4 increments, the last of them partial — so $800 comes off $6,500 of interest, leaving $5,700. With one gate failed — "Final assembly in the U.S." answered no — the same numbers produce $0. Like the senior deduction, it is claimed on Schedule 1-A and never reduces AGI or MAGI.

Standard Deduction Calculator

The Standard Deduction Calculator calls standardDeduction2026({ status, taxpayer65, taxpayerBlind, spouse65, spouseBlind, dependent, seniorBonus }). Inputs: one of five statuses (the four above plus a qualifying surviving spouse), the age-65 and blindness conditions for each spouse, an optional dependent's earned income, and an optional MAGI to stack the senior deduction on top for display. Each condition adds $2,050 for single and head of household filers or $1,650 per condition per spouse for every other status; a dependent's deduction is the greater of $1,350 or earned income plus $450, never more than the base. Example, head of household, 2026, aged 65: $24,150 plus $2,050 is $26,200. Example, married filing jointly, 2026, one spouse both 65 and blind: $32,200 plus 2 × $1,650 is $35,500. The senior-bonus stacking view is refused for surviving spouses rather than guessed at. The base amounts are the same 2026 figures the tax-year data file holds — the build asserts it — and they already include OBBBA's permanent increase.

Charitable Deduction Calculator

The Charitable Deduction Calculator calls charitableDeduction(input) on one of two input shapes. Non-itemizers supply status, cash gifts to public charities, and any gifts to donor-advised funds or supporting organizations (which are excluded); the deduction is the lesser of the cash gifts and $2,000 joint or $1,000 for everyone else, claimed on Schedule 1-A. Itemizers supply status, AGI (may be negative), and total contributions; a floor of 0.5% of AGI absorbs the first slice of the year's giving, and an optional § 68 check — single and married filing jointly only — applies the 2/37 haircut to all itemized deductions above the top bracket's start ($640,600 single, $768,700 joint), capping the benefit at 35¢ per dollar. Example, married filing jointly itemizer, 2026: $150,000 of AGI and $6,000 of contributions — the floor absorbs $750.00, leaving $5,250.00 deductible. Example, head of household non-itemizer, 2026: $900 of cash gifts against a $1,000 cap is $900. The itemizer fork assumes gifts are within the AGI percentage ceilings — in the data file's own words, "AGI percentage ceilings still apply on top of the 0.5% floor." — and does not model the ordering of the floor across property types.

What the models do not include

Deliberately excluded everywhere: state and local income taxes; tax credits (the child tax credit, the earned income credit, education credits — none is modeled); AMT; QBI and other business deductions; multi-state or part-year situations; and the Form 2210 underpayment penalty. Itemized deductions are modeled only where a tool says so — the SALT cap and the charitable itemizer fork — and the ordinary-income tools assume the standard deduction. Long-term capital-gains bands are modeled by the capital-gains and crypto tools only; the ordinary-income tools treat all income as ordinary. Every page states its own exclusions and carries a "not tax advice" note, this one included. These are planning estimates of the federal core — your actual liability is determined when you file.

Worked examples can't drift

The numbers in each page's explanation are computed at build time by the very same engine that runs the interactive calculator, not typed in by hand. If a bracket or deduction in the data file changed, the copy would change with it (or the build would fail), so the documentation cannot silently disagree with the tool.

The examples on this page work the same way, and go one step further: each one is paired with an assertion about the shape of its result — that the capital-gains example still straddles two bands, that the bonus example still reaches the wage base, that the senior and SALT examples still sit inside their phase-outs. If a future data-file update moved an example out of the situation its sentence describes, the build would stop rather than publish a sentence that had quietly become untrue.

Tested against reference figures

The engine is covered by automated tests that check it against hand-computed reference values — bracket-by-bracket sums, the FICA wage-base cap, the 401(k)/FICA interaction, the self-employment base and cap, and sales-tax round-trips. Structural tests also verify each tax year's data (strictly increasing thresholds, the 7 statutory rates). If you believe a result is wrong, see the contact page — confirmed issues are fixed in the engine and locked in with a new test.

Sources

The figures and rules on this site come from primary federal sources, not secondary summaries:

  • Income-tax brackets & standard deductions — IRS annual inflation adjustments: Rev. Proc. 2024-40 (I.R.B. 2024-45) for tax year 2025 and Rev. Proc. 2025-32 for tax year 2026. The 2025 standard deductions reflect the One Big Beautiful Bill Act.
  • Long-term capital-gains breakpoints — Rev. Proc. 2024-40 § 2.03 (2025) and Rev. Proc. 2025-32 § 4.03 (2026).
  • Social Security & Medicare (FICA) — the statutory FICA rates; the Social Security wage base is set annually by the SSA (Contribution and Benefit Base).
  • Bonus / supplemental withholding — the percentage method in IRS Pub. 15 (Employer's Tax Guide).
  • Estimated taxes & due dates — IRS Pub. 505 and Form 1040-ES.
  • Modified AGI (MAGI) — IRS Pub. 590-A (Worksheets 1-1 and 2-1), the Instructions for Form 8962 (Worksheet 1-1), and SSA POMS HI 01101.010.
  • Digital-asset capital gains — IRS Notice 2014-21, the Form 1099-DA instructions, and Tax Topic 559.
  • No Tax on Tips & Overtime — the enacted statute, 26 U.S.C. § 224 (qualified tips) and § 225 (qualified overtime), plus IRS newsroom guidance on the One Big Beautiful Bill Act deductions.
  • OBBBA deductions for 2026 — the enacted statute (P.L. 119-21) and the Internal Revenue Code as amended, Rev. Proc. 2025-32, and IRS newsroom and topic pages, each cited constant by constant in the OBBBA data file; figures last verified 2026-08-18.

Every consequential number should be confirmed against the current IRS and SSA publications for your tax year; where a page relies on a specific worksheet or notice, it links that source directly.

Not tax advice: everything on this page — the formulas, the input ranges, and the worked examples — describes planning estimates of the federal core, computed from the numbers a user enters, with the exclusions listed above; none of it is tailored to your situation. Consult a tax professional or IRS.gov before acting on any figure. Values entered into the calculators are processed locally in your browser and never transmitted. This is the methodology page: each tool's scope is stated in the calculator-by-calculator section above; see the disclaimer for the site-wide cautions and the guides for the longer explanations.