Estimated Tax Safe Harbor: 100% vs 110% Rule
To generally avoid the 2026 underpayment penalty, pay in the smaller of 90% of your 2026 tax or 100% of your 2025 tax. The prior-year figure becomes 110% if your 2025 AGI was more than $150,000 ($75,000 if married filing separately for 2026). AGI of exactly $150,000 stays at 100%.
"Safe harbor" is the phrase tax pros use for the minimum you can pay during the year and still generally avoid the estimated tax penalty. It's useful because you don't need to predict your income perfectly. You need to hit one of two targets. This post explains both, when 100% becomes 110%, and which target is usually easier.
What is the estimated tax safe harbor?
Under IRC §6654(d) and the 2026 Form 1040-ES, your required annual payment for 2026 is the smaller of:
| Target | Percentage | Based on |
|---|---|---|
| Current-year safe harbor | 90% | the tax on your 2026 return |
| Prior-year safe harbor | 100% | the tax on your 2025 return |
| Prior-year safe harbor, higher income | 110% | the tax on your 2025 return, if 2025 AGI was more than $150,000 (more than $75,000 if married filing separately for 2026) |
You pay the required annual payment through withholding and estimated payments, generally in four equal installments. For 2026 those are due April 15, June 15, September 15, 2026 and January 15, 2027.
"Tax" means total federal tax, including self-employment tax, less refundable credits. It is not your refund or balance due.
When does the 110% rule apply?
Three details decide it, and each one catches people out.
- It's last year's AGI. The test uses your 2025 adjusted gross income, not your 2026 income. A big 2026 does not trigger 110% for 2026.
- It's "more than". The 1040-ES wording is "more than $150,000". AGI of exactly $150,000 stays at 100%. At $150,001 it becomes 110%.
- The threshold is the same for single and joint filers. It is $150,000 whether you file single, head of household or jointly. Only married filing separately (for 2026) uses $75,000.
Here is the "more than" rule in numbers. A single freelancer expects $180,000 of 2026 profit and had $30,000 of 2025 tax. We ran both versions through our Quarterly Estimated Tax Calculator:
| 2025 AGI | Prior-year % | Prior-year target | Per quarter | 90% of 2026 tax ($47,058.40) |
|---|---|---|---|---|
| $150,000 | 100% | $30,000 | $7,500 | $42,352.56 |
| $150,001 | 110% | $33,000 | $8,250 | $42,352.56 |
One dollar of AGI adds $3,000 to the target. Either way, the prior-year target is well below 90% of this year's tax, so it is the one to use.
And a married-filing-separately example: $90,000 of 2026 profit, $14,000 of 2025 tax, 2025 AGI of $80,000. Because $80,000 is more than $75,000, the prior-year target is 110% × $14,000 = $15,400, or $3,850 a quarter. That is still lower than 90% of the estimated 2026 tax ($17,384.34).
Which safe harbor should I use: current year or prior year?
You can use whichever is smaller, and the calculator shows both side by side. As a rule of thumb:
- Income going up? The prior-year target is usually lower and it's a known number. You can read it off last year's return. You don't have to guess.
- Income going down? The 90% current-year target may be lower, but it depends on an estimate you can get wrong.
Three 2026 scenarios, all single with profit only and the standard deduction:
| Scenario | 2026 tax | 90% of 2026 | Prior-year target | Required annual payment | Basis |
|---|---|---|---|---|---|
| Growing: $85,000 profit; 2025 tax $15,000, AGI $70,000 | $17,800.03 | $16,020.03 | $15,000 (100%) | $15,000 | Prior year |
| High income: $250,000 profit; 2025 tax $50,000, AGI $210,000 | $66,360.02 | $59,724.02 | $55,000 (110%) | $55,000 | Prior year |
| Falling: $50,000 profit; 2025 tax $30,000, AGI $140,000 | $9,732.07 | $8,758.86 | $30,000 (100%) | $8,758.86 | Current year |
In the falling-income case, the 90% target saves a lot of cash during the year. But if the year turns out better than expected, 90% of the actual tax will be higher than the estimate. Some people pay a little extra as a buffer.
Does the safe harbor mean I won't owe anything in April?
No. The safe harbor generally protects you from the penalty. It doesn't cover the tax. If your income grew, you'll owe the difference when you file:
| Scenario | 2026 tax | Paid via safe harbor | Due with the 2026 return by April 15, 2027 |
|---|---|---|---|
| $85,000 profit, 100% of 2025 | $17,800.03 | $15,000 | about $2,800 |
| $250,000 profit, 110% of 2025 | $66,360.02 | $55,000 | about $11,360 |
That April balance is why we suggest setting money aside even while you pay only the safe harbor. The calculator gives a "set aside" percentage for this: about 20.9% of each dollar of profit in the $85,000 case and about 26.5% in the $250,000 case, federal only.
When is the prior-year safe harbor not available?
The prior-year option needs a 2025 return that covered a full 12 months. It also can't be based on a return you never filed. In those cases only the 90% current-year target applies.
Special rules also apply if at least two-thirds of your gross income for 2025 or 2026 is from farming or fishing. Then the current-year percentage is 66⅔% instead of 90%, and the 110% rule doesn't apply.
The opposite case is the zero-tax exception. If your 2025 total tax was zero (or you didn't have to file), 2025 was a full year and you were a US citizen or resident all year, you don't have to pay 2026 estimated tax at all. See First Year Freelancing: How to Handle Estimated Taxes.
What if I missed the safe harbor for earlier quarters?
The penalty is figured separately for each installment, for the days it stays unpaid, at the IRS underpayment rate (7% a year for October 1 to December 31, 2026, per IR-2026-98). Paying the shortfall now generally reduces it. If you have a W-2 job, extra withholding is generally treated as paid evenly through the year (IRC §6654(g)), so it can help earlier quarters too.
If you want someone to work out the right target every quarter, RAHA's Bookkeeping + Quarterly Estimates service does exactly that, alongside monthly bookkeeping. It is a fixed price, quoted upfront. For the whole picture, read our pillar guide to quarterly estimated taxes.
Frequently asked questions
Is the 110% rule based on 2025 or 2026 income?
- The test looks at your prior-year AGI. For 2026 estimated payments, that is the AGI on your 2025 return.
If my 2025 AGI was exactly $150,000, do I use 100% or 110%?
100%. The rule applies only when AGI is more than $150,000.
Is the threshold $300,000 for married couples filing jointly?
No. It is $150,000 for joint filers too. Only married filing separately uses a lower figure, $75,000.
Can I switch between the 90% and prior-year methods during the year?
The required installment for each period is based on the smaller of the two annual targets. You don't elect one in advance. Many people start with the prior-year target because it's known, then check it against a current-year estimate later in the year.
Does withholding count toward the safe harbor?
Yes. Withholding and estimated payments both count. Withholding is generally treated as paid evenly across the four due dates.
Do states use the same 100%/110% rule?
Not necessarily. Many states set their own estimated tax rules and percentages. Check your state tax agency's instructions. Our calculator covers federal tax only.
Sources
- IRC §6654(d) (required annual payment) and §6654(g) (withholding): https://www.law.cornell.edu/uscode/text/26/6654
- IRS, 2026 Form 1040-ES, Estimated Tax for Individuals: https://www.irs.gov/pub/irs-pdf/f1040es.pdf
- IRS, Topic no. 306, Penalty for underpayment of estimated tax: https://www.irs.gov/taxtopics/tc306
- IRS, About Form 2210: https://www.irs.gov/forms-pubs/about-form-2210
- IRS, interest rates for the fourth quarter of 2026: https://www.irs.gov/newsroom/interest-rates-remain-the-same-for-the-fourth-quarter-of-2026
This guide provides general information for educational purposes and is not tax, legal or accounting advice. Consult a qualified professional before acting.
