Estimated tax safe harbour calculator
What you must have paid by the next quarterly deadline for an underpayment penalty to be impossible — which is usually far less than you will eventually owe.
US Uses United States federal tax rules
Updated August 27, 2026
What this protects you from, and what it does not
The safe harbour protects you from the underpayment penalty. It does not protect you from the bill.
Those are different things, and conflating them is the single most expensive misunderstanding in freelance tax. Pay the safe-harbour amount and the IRS cannot charge you a penalty no matter how much you end up earning — but you will still owe the rest of the tax when you file in April. A balance is not a penalty. It is simply the tax, paid later.
So the safe harbour is best understood as permission not to overpay, not permission not to save. Pay this amount to the IRS quarterly, keep setting aside your full estimated share in a separate account, and settle the balance in April out of that account.
The two tests
You are protected if your payments across the year reach either of:
- 90% of the tax you end up owing this year — accurate, but it requires you to predict the year, which freelance income does not permit.
- 100% of the total tax on last year's return, rising to 110% if last year's AGI was over $150,000 ($75,000 if married filing separately) — a number that already exists and requires no forecast at all.
You only have to meet the lower of the two. That matters far more than it sounds, and it is where most published calculators go wrong: they implement the prior-year rule only. If you are having a worse year than last, the prior-year figure is not your requirement — 90% of this year's smaller tax is, and it can be thousands less. Filling in the optional "this year's expected tax" field above is the only thing that can reduce what this tool tells you to pay.
Why withholding is the trick worth knowing
Estimated payments count from the day you make them. Withholding does not. Tax withheld from a W-2 is treated as paid in equal parts on each of the four deadlines, regardless of when it was actually withheld.
The consequence is genuinely useful: if anyone in your household has a W-2 job, filing a new W-4 in October to withhold more can retroactively cure a shortfall from April. An estimated payment cannot do that. It is the one lever that reaches backwards, and it is why the withholding field above asks for your expected full-year figure rather than the amount withheld so far.
The deadlines are not quarters
They are widely called quarterly and they are not evenly spaced — the second period is two months long and the fourth is four.
| Instalment | Income earned | Payment due |
|---|---|---|
| Q1 | Jan 1 – Mar 31 | April 15, 2026 |
| Q2 | Apr 1 – May 31 | June 15, 2026 |
| Q3 | Jun 1 – Aug 31 | September 15, 2026 |
| Q4 | Sep 1 – Dec 31 | January 15, 2027 |
Each deadline carries a quarter of the annual requirement, so by the September payment you should be three quarters of the way there. That cumulative framing is what this calculator computes, and it is why "I paid a lot in April" does not necessarily mean you are covered now.
When no payment is required at all
Two cases, both common and both worth checking before you send money:
- You will owe under $1,000 when you file. No penalty applies below that, regardless of the tests above.
- You had no tax liability last year, you were a US citizen or resident for the whole year, and that year covered twelve months. In that case there is no penalty this year at all — which is why a genuine first year of self-employment usually carries no estimated-payment obligation, and why entering 0 for last year's tax above returns a requirement of zero.
What this does not model
- State estimated tax. Most states with an income tax run their own quarterly system with their own safe harbour, and the rules differ. This is federal only.
- The annualised income instalment method. If your income is heavily seasonal, Form 2210 Schedule AI lets you match payments to when you actually earned the money, which can beat the even-quarters approach. It is considerably more work and needs records by period.
- The penalty itself. This tells you how to avoid it, not what it would cost if you do not. It is charged like interest — on the amount you were short, for the days you were short, at the federal short-term rate plus three points.
An estimate for planning, not tax advice. The figures come from your own inputs and never leave your browser.