Your remaining estimated tax spread evenly across the quarters left, with the running total paid after each instalment. This is an even split for planning only — many authorities set staggered due dates and safe-harbour percentages rather than four equal payments, so confirm the official schedule.
Quarter
Payment
Cumulative paid this period
Quarter 1
6,000
6,000
Quarter 2
6,000
12,000
Quarter 3
6,000
18,000
Total remaining
18,000
18,000
Estimates only — not financial, tax, or professional advice.
100% private — every number you enter is calculated in your browser and never sent to our servers.
What it calculates: Per-quarter payment, Remaining tax due, Annual estimate, Quarters remaining.
Updated 5 June 2026 · Transparent assumptions
$18,000 left over three quarters is $6,000 each, not $4,500
An annual estimate of $24,000 with $6,000 already paid leaves $18,000. Spread across the three remaining quarters that is $6,000 each — higher than the $6,000-a-quarter even split only because the first quarter was short. Recomputing against quarters remaining, rather than against four, is the whole point of this calculation.
The catch-up does not undo a missed instalment. Most systems compute the underpayment penalty per quarter, so paying extra later covers the liability but does not refund the interest already accrued on the earlier shortfall. The penalty is usually modest, but it is not zero and it is not avoided by settling in full at filing.
The instalment periods are uneven in most systems
Estimated tax periods rarely divide the year into four equal parts. In the US the instalments cover January to March, April to May, June to August and September to December, with due dates in April, June, September and the following January. The second period is two months long and the fourth is four.
That matters for anyone matching payments to income as it is earned. Treating the year as four equal quarters when the periods are uneven produces instalments that are late relative to the actual deadlines, and lateness is what the penalty is computed on.
A forecast made in January is rarely right by September
The annual figure entered here is a forecast, and for variable income it will drift. Revising it each quarter against actual income to date, and recomputing what remains across the quarters left, keeps the instalments tracking reality rather than a January assumption.
Revising downward is as important as revising upward. A business having a poor year that keeps paying instalments sized for a good one is lending money it may need, and the excess will not return until the return is filed and processed.
Whether the annual estimate is right in the first place
This page divides a number you supply; it does not test whether that number is correct. The annual estimate should include income tax, self-employment or social contributions, and any state or local liability that is also paid by instalment — omitting the last is a common cause of an unexpected balance at filing.
Nor does it check the safe harbour. Paying the prior year\u2019s liability generally avoids a penalty regardless of how the current year turns out, and for anyone with volatile income that is usually the safer target than an accurate forecast of a year that has not happened yet.
Sources & References
Figures on this page are checked against primary, authoritative sources. Links open in a new tab.
Tax rules vary by country, state, tax year, filing status, income type, deductions, and exemptions. This calculator is educational and uses the values you enter. Always verify final tax treatment with official sources or a qualified tax professional.
Published the calculator with its formula, worked example, assumptions, limitations and a bespoke guide, and added an automated formula test suite covering it.
Tested that the remaining liability divides across the quarters actually left rather than across four, which is what makes catching up work.
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