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.
Calculated in your browser — the numbers you enter are never sent to our servers.
What it calculates: Per-quarter payment, Next payment, US IRS method, Remaining tax due, Annual estimate.
$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’s 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.
Frequently Asked Questions
Who needs to pay quarterly taxes?
Typically the self-employed, freelancers, investors, and businesses whose tax is not fully collected through withholding. Paying in instalments spreads the cost and helps avoid a large balance and underpayment charges at year-end.
How do I estimate my annual tax?
Project your taxable income for the year, apply your expected effective rate, and adjust for credits. Update the estimate as the year progresses so your instalments track your actual income.
What if my income changes during the year?
Recompute the annual estimate and re-divide the new remaining balance over the quarters left. Raising or lowering later instalments keeps you on track without overpaying or underpaying.
Are the quarters always equal?
Not always. Some authorities require staggered percentages by due date rather than four equal payments. This tool uses an even split, so check whether your jurisdiction expects uneven instalments.
What happens if I underpay?
Many systems charge interest or a penalty on underpaid instalments. This calculator only sizes the payments; it does not compute underpayment charges, which depend on your local rules.
Sources & References
Figures on this page are checked against primary, authoritative sources. Links open in a new tab.
The remaining balance is spread evenly across the quarters left; some systems use uneven safe-harbour percentages. For US individuals the next-payment figure follows the IRS regular installment method instead (Pub. 505), which catches an increase up in the next period.
The annual estimate, payments, and number of quarters are your own figures, not authoritative schedules.
Withholding already collected is counted within the amount paid so far where relevant.
Results are estimates for general and educational use.
Where it stops
Due dates, instalment percentages, and safe-harbour rules vary by country and tax year.
An even split may differ from the staggered percentages some authorities require (for example 15/45/75/100%).
Penalties and interest for underpayment are not calculated here.
This tool does not file returns, schedule payments, or confirm compliance.
Related Calculators
Estimated Tax PaymentThe quarterly payment implied by expected income and rate, after whatever is already being withheld.
Self-Employment TaxSE tax on net profit, the deductible half, and the quarterly estimated payments it implies.
Corporate TaxCorporation tax on taxable profit, with any surcharge and the effective rate it produces.
Dividend TaxTax on dividend income at the rate that applies to it, with the net actually received.
IndexationIndexed cost from the two years' cost inflation index, the gain that survives it, and the tax on that gain.
Average Cost BasisOne blended cost per unit across up to three purchase lots bought at different prices.
India GSTGST added or extracted, split into CGST and SGST or charged as IGST, with input tax credit applied.
UK VATVAT at the standard, reduced or zero rate, added to a net price or extracted from a gross one.
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.
Frequently Asked Questions now show on the page: 5 answers, checked in a page-by-page audit.
What the calculation assumes and where it stops now show on the page.
Added the next payment under the IRS regular installment method (Pub. 505): an even split underpays the next period after a mid-year increase. Checked against the IRS example, $1,800 refigured to $4,100 after $900 paid: $2,175, then $1,025.
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