Quarterly estimated tax calculator
What to send the IRS each quarter, based on the safe harbour that makes an underpayment penalty impossible rather than on a forecast you cannot verify.
Covers tax year 2026 · rates as at 2026-01-01
Pay each quarter
Estimate$4,500.00
18,000 across four instalments to reach the safe harbour
- Safe harbour target
- $18,000
- Self-employment tax
- $13,423
- Projected tax for the year
- $24,017
| Net profit | $95,000 |
|---|---|
| Self-employment tax | $13,423 |
| Federal income tax | $10,593 |
| 90% of this year | $21,615 |
| 100% of last year | $18,000 |
| Still to pay this year | $18,000 |
- Last year's tax is the cheaper safe harbour here, and it is a known number — you cannot be penalised for paying it even if this year turns out much bigger.
- Withholding from a job counts as paid evenly across the year, so increasing it late can fix an underpayment that quarterly instalments cannot.
Paying 100% of last year’s $18,000 tax protects you from any penalty even if this year turns out far larger — the safe harbour is about certainty, not accuracy.
Over the life of it
How this is calculated
Two safe harbours, and you only need the cheaper one
Pay 90% of this year’s tax, or 100% of last year’s — 110% if last year’s AGI exceeded $150,000. Meeting either makes the underpayment penalty inapplicable no matter what you eventually owe.
required = min(90% × this year, 100% or 110% × last year)The prior-year figure is the reliable one
It is a known number from a filed return. The 90% test depends on forecasting a year you have not finished, and a good year that arrives in Q4 can breach it retroactively across all four instalments.
Withholding beats instalments for fixing a shortfall
Estimated payments are credited on the date paid, so a Q1 shortfall accrues penalty even if Q4 overpays. Withholding from a job is treated as paid evenly across the whole year, so raising it in December can repair an underpayment from January.
Worked example: $95,000 of self-employment profit, $18,000 of tax last year
| Net profit | $95,000 |
|---|---|
| Last year's tax | $18,000 |
| Last year's AGI | $120,000 |
| Withheld | $0 |
| Safe harbour rate | 100% |
|---|---|
| Target | $18,000 |
| Per quarter | $4,500 |
If prior-year AGI had been $160,000 the safe harbour would rise to 110% — $19,800, or $4,950 a quarter — for exactly the same current-year income.
What this assumes
- Federal tax only, no state estimated payments.
- Even income across the year, not annualised.
- Standard deduction with no credits.
- Sole proprietor filing Schedule C.
Where this commonly goes wrong
- The four due dates are not quarterly — 15 April, 15 June, 15 September and 15 January leave gaps of three, three, four and two months.
- A first profitable year has no prior-year safe harbour worth using if last year’s tax was near zero, so the 90% test is the only protection and forecasting matters.
- State estimated tax is separate and has its own deadlines and penalties; meeting the federal safe harbour does nothing for your state.
Questions
How much should I pay in quarterly estimated tax?
Enough to hit the safe harbour: 90% of this year’s tax or 100% of last year’s, whichever is lower. On $18,000 of prior-year tax that is $4,500 a quarter, and no penalty can apply however much you eventually owe.
What is the safe harbour rule?
Pay 90% of the current year’s tax or 100% of the prior year’s — 110% if prior-year AGI exceeded $150,000 — and the underpayment penalty cannot be charged. It is protection from the penalty, not from the tax itself.
When are estimated tax payments due?
15 April, 15 June, 15 September and 15 January of the following year. Despite the name they are not evenly spaced: the gaps are three, three, four and two months.
What happens if I underpay one quarter?
Penalty accrues from that instalment date, and overpaying later does not undo it. Estimated payments are credited when made, which is why an early miss is more expensive than a late one.
Can I use withholding instead of estimated payments?
Yes, and it is often better. Withholding from a job or a pension is treated as paid evenly across the whole year, so increasing it in December can repair an underpayment dating back to January.
Do I need to pay estimates in my first year of business?
If you expect to owe $1,000 or more, yes. With little or no prior-year tax the 100% safe harbour is not useful, so you have to forecast — which makes a conservative estimate worth more than an accurate one.
Related tools
Sources
- IRS — Estimated taxes
- IRS — Publication 505, tax withholding and estimated tax
- IRS — Underpayment of estimated tax
- IRS — Standard deduction for 2026
- IRS — Rev. Proc. 2025-32 §3.03
- IRS — Net investment income tax thresholds
- SSA — Medicare tax rate
- IRS — Additional Medicare tax thresholds
- IRS — Self-employment tax rates
Estimate only, based on published IRS figures for tax year 2026. Not tax or legal advice. Confirm your position with the IRS, a CPA, or an enrolled agent.
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