Estimated Tax Safe Harbor Calculator
The least you can pay in estimated taxes and still owe no underpayment penalty — which rule you're under, what's left after withholding, and what to send each quarter.
Ben / Reviewed Sep 27, 2026 / v2.0.0
Results
Showing the numbers you calculated- Safe harbor amount
- $25,000.00
- 100% of last year's tax ($25,000.00). That's less than 90% of this year's ($27,000.00).
- Next payment
- $4,250.00
- Due 04/15/2026
- Still to pay in estimates
- $17,000.00
- Safe harbor − withholding − payments so far
- 90% of this year's tax
- $27,000.00
- Last year's test
- $25,000.00
- 100% of last year's tax
- Left to pay when you file
- $5,000.00
- The safe harbor avoids the penalty, not the tax
Your payment plan
Upcoming payments catch up anything you're behind on first, then keep pace with 25% of the safe harbor per installment.
| Installment | Due | Status | Pay |
|---|---|---|---|
| Q1 | 04/15/2026 | Upcoming | $4,250.00 |
| Q2 | 06/15/2026 | Upcoming | $4,250.00 |
| Q3 | 09/15/2026 | Upcoming | $4,250.00 |
| Q4 | 01/15/2027 | Upcoming | $4,250.00 |
What this does
If you have income without withholding — freelance work, a side business, investments — the IRS wants its money during the year, not in April. Pay too little along the way and you owe an underpayment penalty, even if you pay everything when you file.
The good news: you don't have to predict your tax perfectly. There's a "safe harbor" — a minimum that makes you penalty-proof. This finds yours, subtracts your withholding, and tells you what to send each quarter.
How the math works
The safe harbor is the smaller of two numbers:
90% of this year's tax 100% of last year's tax (110% if last year's AGI was over $150,000)
Last year's number is usually the easy one, since you already know it. Pay at least the safe harbor through withholding and estimates — 25% by each due date — and there's no penalty.
Two outs: if you owed nothing last year, there's no penalty this year. And if this year's tax minus withholding is under $1,000, there's no penalty either.
Withholding counts as if it were paid evenly all year, even if it came out of your last paycheck in December. That makes raising your withholding the easiest way to fix a quarter you missed.
Check my math: a worked example
Last year's tax was $25,000 on $120,000 of AGI. This year looks like $30,000, with $8,000 withheld from a paycheck.
- 90% of this year: $27,000.00.
- 100% of last year: $25,000.00 (AGI was under $150,000, so 100%).
- Safe harbor: the smaller one, $25,000.00.
- Withholding covers $8,000.00, leaving $17,000.00 in estimates.
- Plan: $4,250.00 by 04/15/2026, $4,250.00 by 06/15/2026, $4,250.00 by 09/15/2026, $4,250.00 by 01/15/2027.
- You'd still owe $5,000.00 when you file — the safe harbor protects you from the penalty, not the tax.
These numbers come straight from the calculator using its example inputs — if the math ever changes, this example changes with it.
Mistakes I see a lot
- Using this year's AGI for the 110% test. It's last year's AGI that matters.
- Subtracting withholding from "tax." Withholding is a payment; the tax is the total on the return.
- Paying everything in January. The penalty is figured per quarter, so a late catch-up still costs something for the months you were behind.
- Assuming a refund last year means you're fine. The test is the tax, not the refund.
- Forgetting state estimates. Most states have their own rules and due dates.
Questions people ask
- When are the payments due?
- Mid-April, mid-June, mid-September, and mid-January of the next year. When a due date lands on a weekend or holiday, it moves to the next business day — the calculator uses the actual dates.
- What does the penalty actually cost?
- It works like interest: the IRS underpayment rate (the federal short-term rate plus 3%) on each late amount, for the days it's late. Annoying, not catastrophic — but easy to avoid.
- My income is lumpy. Do I really have to pay 25% each quarter?
- Not necessarily. The annualized income installment method (Form 2210, Schedule AI) lets you pay based on what you'd actually earned by each due date. It takes more work, and this calculator doesn't do it.
- I missed the first two payments. Now what?
- Catch up as soon as you can — the plan puts the catch-up in your next payment. If you have a W-2 job, bumping your withholding for the rest of the year is even better, because withholding counts as paid evenly across all four quarters.
- Does this include self-employment tax?
- Yes. The tax that matters is your total tax — income tax plus self-employment tax — after credits. Use the Self-Employment Tax calculator for that part.
Assumptions and limits
- Federal only (IRC §6654). States have their own rules.
- The required annual payment is the lesser of 90% of this year's tax or 100% of last year's — 110% of last year's if last year's AGI was over $150,000 ($75,000 married filing separately). The prior-year test needs a full 12-month prior year with a return filed.
- No penalty at all if you owed no tax last year (full year, U.S. citizen or resident), or if this year's tax minus withholding is under $1,000.
- "Tax" means total tax (including self-employment tax) after nonrefundable credits, minus refundable credits like the EITC — the way Form 2210 figures it. Withholding is a payment, not a reduction of tax.
- Withholding is treated as paid evenly on the four due dates, which is the default rule. Estimated payments count when you make them.
- The regular installment method: 25% of the required annual payment by each due date. The annualized income method (for lumpy income) can lower early installments but isn't modeled here.
- Farmers and fishermen (66⅔% rule) and fiscal-year filers aren't covered.
Disclaimer: Educational and planning use only. Results depend on what you enter and may not match your lender, your tax return, or professional accounting treatment. Informational content + opinions only — not tax/legal advice. Tax rules change and have exceptions this calculator doesn't cover — confirm current rules and your specific facts before relying on the result.