Quarterly Estimated Tax Calculator

What estimated taxes are, and why they're quarterly

Employees have tax withheld from every paycheque. When you work for yourself, nobody withholds anything — so most tax systems expect you to pay your tax in instalments through the year rather than in one lump at filing time. In the US these are the quarterly estimated tax payments; other countries have their own payment-on-account schemes. Miss them and you can face interest or an underpayment penalty even if you eventually pay in full.

This calculator turns your expected annual tax into the amount to send each remaining period. Enter the net profit you expect for the year, the effective tax rate you want to reserve against it, and anything you've already paid. It spreads the rest evenly across the quarters you have left.

Picking an effective tax rate to reserve

The effective rate is the single percentage that, applied to your profit, covers everything you owe on it — income tax plus any self-employment or social charges, across all the brackets that apply to you. It is not your top marginal bracket; it is the blended average, and it is yours to set. Many self-employed people reserve somewhere between 25% and 30% of profit, but the right figure depends entirely on your country, income, and deductions.

Because the rate is an input you control, this tool asserts no official figures — work yours out from last year's return or a fuller tax estimate, then use it here. If you've already paid some instalments, enter that total: the calculator subtracts it first, so a quarter where you've front-loaded payments can come out lower, or zero.

The safe harbour is the number that actually protects you

Estimating this year's tax is guesswork, because you do not know yet what you will earn. The rules account for that with a safe harbour: pay at least 90% of what you end up owing this year, or 100% of what you owed last year — whichever is smaller — and you avoid the underpayment penalty even if your final bill is much larger.

For anyone whose income swings, the prior-year figure is the more useful target, because it is a number you already know. Take last year's total tax, divide by four, pay that each quarter, and the penalty is off the table regardless of how good this year turns out to be. You may still owe a balance at filing time — the safe harbour prevents a penalty, not a bill.

There is also a floor: if you expect to owe less than $1,000 after withholding and credits, the penalty does not apply at all. Higher-income taxpayers face a stricter version of the prior-year test, so check Publication 505 if you are well into six figures.

Set the money aside on the day it arrives

The mechanical failure behind most missed quarterly payments is not forgetting the date. It is that the money was spent by the time the date came. A quarterly payment is not something you fund out of that month's income; it is something you fund out of every payment across the quarter.

The fix that works is boring and automatic: a second business account, and a fixed percentage of every client payment moved into it the day the payment lands. Twenty-five to thirty percent covers self-employment tax plus federal income tax for most people at moderate profit. When the due date arrives, the money is already there and the payment is an administrative act rather than a financial event.

If your income is uneven — a large project in one quarter, nothing in the next — the annualised income method lets you pay in proportion to when you actually earned, instead of four equal instalments. It is more paperwork, and it is worth it when one quarter carries most of your year.