Quarterly Tax Calculator

This page documents what the calculator above actually does: it estimates your federal income tax and self-employment tax for the year with the same engines as the rest of the site, applies the Form 1040-ES safe harbor, and splits what you must prepay into four installments on the year's published due dates. For the mechanics of the self-employment tax that feeds it — both halves of Social Security and Medicare, and the deductible half the engine subtracts for you — see the companion guide Self-Employment Tax, Explained; the full set of explainers is collected on the guides page.

The worked example, step by step

A single freelancer expecting $80,000 of Schedule C profit in 2026: self-employment tax comes to $11,303.64, and after subtracting the deductible half ($5,651.82) and the $16,100 standard deduction, the brackets charge $7,526.60 of income tax — $18,830.24 of estimated federal tax in total. The safe harbor is the lesser of 90% of that ($16,947.22) or 100% of the $9,000 prior-year tax ($9,000.00) — so the required annual payment is $9,000.00, or $2,250.00 per installment, due April 15, 2026, June 15, 2026, September 15, 2026, and January 15, 2027. Every figure is computed by the same tested engine as the calculator above. The remaining $9,830.24 is simply owed at filing time, penalty-free, because the safe harbor was met.

Why the safe harbor is the number that matters

The IRS does not require you to prepay your exact tax — it requires the safe-harbor amount: the lesser of 90% of this year's tax or 100% of last year's (110% if last year's AGI topped $150,000). For a freelancer whose income is growing, the prior-year option is the planning gift: last year's smaller tax bill sets this year's required payments, and the growth is settled in April without penalty. These percentages and the $1,000 minimum were verified against IRS Publication 505 (2026) and the Form 1040-ES instructions, which remain the controlling sources.

The lesser-of rule, both directions

The word lesser is doing the work. The engine computes both safe harbors — 90% of this year's estimated tax and 100% of last year's total tax — and the required annual payment is whichever is smaller, so the rule always resolves in your favor. Which one wins depends on the direction your income moved. In the flagship example above, income is growing: this year's tax ($18,830.24) is larger than last year's, so 100% of the $9,000 prior-year tax ($9,000.00) undercuts 90% of the current figure ($16,947.22) and becomes the target — last year's smaller bill sets this year's required payments.

Run it the other way. A single freelancer expecting $50,000 of profit this year, down from a $120,000 prior-year AGI that carried $15,000 of tax: this year's estimated tax is $10,460.89, so 90% of it ($9,414.80) is now the lesser of the two against 100% of last year ($15,000.00). The required annual payment follows the current year down to $9,414.80, or $2,353.70 per installment. When income falls, the prior-year figure would make you overpay, so the rule picks the current-year number instead. Both examples are the same 2026 engine on single filers; only the inputs differ.

When last year's income was higher: the 110% step

The prior-year safe harbor is 100% of last year's tax for most filers, but 110% when last year's AGI was above $150,000 ($75,000 for married filing separately, a status this calculator does not model). The engine reads the prior-year AGI you enter and selects the factor itself. A single consultant, 2026, with $160,000 of expected profit whose prior-year tax was $30,000 on $180,000 of AGI crosses that line: the prior-year factor is 110%, so the prior-year safe harbor is $33,000.00 rather than the $30,000.00 the 100% figure would give. That is still below 90% of this year's $47,028.41 estimated tax ($42,325.57), so the stepped-up prior-year number governs — $33,000.00 for the year, $8,250.00 each quarter. The higher percentage narrows the prior-year advantage for higher earners; it does not remove it.

What feeds the estimate

The current-year estimate reuses this site's engines: the federal bracket math on your AGI after the standard deduction (see where that lands you), plus self-employment tax when you enter freelance profit — including the ½ SE-tax deduction, applied for you. Enter your expected AGI before that deduction; if you also have W-2 wages, put your expected paycheck withholding in the withholding field (estimate it with the Take-Home Pay Calculator). Credits and other taxes are out of scope — the estimate is the federal income + SE core.

When no quarterly payment is required

Two conditions have to hold before the tool reports any vouchers at all, both drawn from the Form 1040-ES rules. First, the expected balance after withholding must be at least $1,000 — below that, no estimated payments are required regardless of the safe harbor. Second, withholding must fall short of the required annual payment; withholding counts toward the safe harbor as though it were paid evenly through the year, so a paycheck that already covers the target leaves nothing to prepay. Consider a single W-2 employee, 2026, with a $5,000 side gig, an expected AGI of $90,000, and $12,000 of federal withholding, whose prior-year tax was $10,000 on $85,000 of AGI. The required annual payment is $10,000.00; because the $12,000 already withheld exceeds it, the calculator reports $0.00 per quarter — withholding alone has met the safe harbor. Raising withholding on a W-2 job is the mechanism behind that result; the tool shows it rather than prescribing it.

A first year with no prior return

The prior-year safe harbor needs a prior-year return that covered all twelve months, so in your first year of self-employment it is simply unavailable and the current-year figure is the only one in play. Leave the prior-year fields blank and the engine computes a single target: 90% of this year's estimated tax. A first-year freelancer expecting $60,000 of profit, single, 2026: estimated tax of $12,989.07 makes the required annual payment $11,690.16, or $2,922.54 per installment. The planning difficulty of a first year is exactly that the safe-harbor shortcut is closed — there is no smaller prior-year number to fall back on — so the estimate rides entirely on how well you have projected the year's income, which is the one input no engine can verify for you.

Four equal installments, four uneven windows

Once the required annual payment is known, the arithmetic of the vouchers is deliberately plain: the tool subtracts expected withholding and divides the remainder into four equal installments. That matches the standard case the IRS assumes — income arriving evenly through the year. The four payment windows themselves are not even, though: they cover roughly January–March, April–May, June–August, and September–December, which is why the due dates sit close together in the middle of the year. For 2026 they fall on April 15, 2026, June 15, 2026, September 15, 2026, and January 15, 2027. Those dates are stored as per-year data rather than derived from a formula, because each one shifts to the next business day when it lands on a weekend or legal holiday and the IRS publishes the shifted date. If your income is lumpy — a fourth-quarter windfall, seasonal work — the annualized income installment method on Form 2210 can match early payments to when the income actually arrived, but that method is out of scope here; this tool models the even-installment case only.

How to read the four figures

The result distinguishes four numbers, and most misreadings come from conflating them. The current-year tax is the full estimated federal income plus self-employment tax in scope — the figure your return reconciles against. The required annual payment is the safe-harbor amount, the lesser of the two harbors, and it is normally smaller than the current-year tax; prepaying it avoids the penalty, it does not settle the bill. The total estimated payments is the required annual payment minus expected withholding — what the vouchers must cover between them — and the quarterly payment is a quarter of that. The gap between the current-year tax and the required annual payment is not an error: it is the balance you expect to owe at filing time, and meeting the safe harbor is what keeps that balance penalty-free. The calculator answers the planning question — how much to send each quarter to stay inside the safe harbor — and leaves the penalty arithmetic, which depends on exactly when each payment lands, to Form 2210, which it does not compute.

Frequently asked questions

Not tax advice: a planning estimate of federal income + self-employment tax only — no credits, no capital-gains rate treatment, no state estimated taxes, no married-filing-separately modeling, no annualized-installment method, and no Form 2210 penalty computation. Safe-harbor rules and due dates verified against IRS Pub. 505 and Form 1040-ES for the supported years; your actual obligations are determined by your full return. Consult a tax professional for your situation. Values are processed locally in your browser and never transmitted. See the methodology page.