Estimated taxes
Estimated taxes, explained: the 90% and 100%/110% safe harbors
Underpay by more than $1,000 and the IRS charges about 7% a year on the shortfall (early 2026 rate). Here is the system that avoids it, with real dollar examples.
The short answer
Pay $50,274 of your tax during the year and the IRS charges you no penalty, even with $16,403 still due in April. That is the safe-harbor deal: pay the smaller of 90% of this year's total tax or 100% of last year's total tax (110% if last year's AGI was over $150,000), through withholding or quarterly estimates spread across four installments, and the §6654 interest charge goes to zero no matter how large the balance. One asymmetry does most of the practical work: withholding counts as paid evenly all year no matter when it lands; estimated payments do not.
Check your position: Safe-harbor status calculator →
Who has to pay estimated tax
The U.S. tax system is pay-as-you-go: tax is due as you earn, not in one April lump sum (IRC §6654). You generally must make estimated payments if you expect to owe at least $1,000 when you file, after withholding and refundable credits. The system bites income with no withholding: capital gains, freelance income, RSU vests under-withheld at the flat 22% rate, interest, dividends, rent, retirement distributions.
The two safe harbors
Section 6654 defines two escape hatches. Clear either and the penalty is zero, no matter how large the April balance:
Harbor 1 — 90% of this year's tax. Pay at least 90% of what your2026total tax turns out to be. Precise, but it asks you to know the year's total in advance.
Harbor 2 — 100% of last year's tax (110% if last year's AGI exceeded $150,000; $75,000 if married filing separately). Last year's total tax is knowable on January 1, which makes it the default for anyone whose income jumps around. The 110% tier up close: the 110% safe-harbor rule, explained →
The rule compares your payments to the smaller of the two targets. If last year's tax was $45,704 and this year's will be $93,787, paying $50,274 (110% of prior) protects you completely. You still owe the $43,513 balance in April, but without the interest charge.
Worked example: the first big vest year usually protects you
Take a single filer with a $180,000 salary who vests $144,000 of RSUs (four quarterly $36,000 vests, the same scenarios as the RSU guide). Last year was salary only: total tax $45,704, AGI $180,000. This year, total tax is $93,787.
His W-4 withholds at the salary-only pace ($45,704 across the year); sell-to-cover takes the flat 22% on the vests ($31,680). Paid during the year: $77,384.
Last year's AGI was over $150,000, so the prior-year target is 110% of $45,704: $50,274. The 90%-of-current-year target is $84,408. The binding target is the smaller: $50,274 — and $77,384 clears it with room.
The April bill is still real: $93,787 minus $77,384 leaves $16,403 due at filing. But the penalty is $0. The first big vest year hurts; it does not penalize.
Worked example: the repeat year flips the harbor
Same person, one year later — a second identical vest year. Now last year's tax is the big one: $93,787, with AGI $324,000, so the prior-year harbor is 110% of that: $103,166. The 90% harbor is 90% of this year's identical $93,787: $84,408. The binding target flips to the current-year harbor: $84,408.
The same $77,384 of withholding now leaves a $7,024 shortfall. Nothing about his behavior changed, but the harbor he coasted on is gone: the binding target jumped from $50,274 to $84,408. The prior-year harbor is one year of protection, not a pattern.
The penalty on that shortfall is interest, not a fine: at the current 7% rate, $7,024 short across the four quarters costs about $330. The fix is a W-4 change. To close a $7,024 gap through withholding: $585 a month from January, $1,171 a month from July, about $270 per biweekly paycheck from October. The April balance drops from $16,403 to $9,379 either way.
The quarterly rhythm, and the withholding asymmetry
Quarterly installments are due April 15, June 15, September 15, and January 15 of the following year, and each covers its own quarter. With lumpy income — a big vest in Q3, a freelance spike in Q4 — you can annualize: compute each quarter's payment from income actually earned to date. The worksheets are in Publication 505.
Two facts decide almost every practical choice:
- Each quarter stands alone. The penalty accrues on each quarter's shortfall from that quarter's due date. A June payment covers Q2; it does not erase Q1.
- Withholding counts as paid evenly, no matter when it lands. Payroll withholding — and withholding on Social Security or retirement distributions — is treated as if one quarter arrived each quarter, even if it all came out in December. Estimated payments count only from their own date forward.
With wages, raising withholding is usually the better lever: no vouchers, no quarterly calendar, and a December W-4 bump retroactively covers Q1. With no wages, quarterly payments are the route, as the freelancer below.
Worked example: the freelancer's version
A freelancer with no W-2 job. Last year she held a $60,000 job: total tax $9,610, AGI $60,000, so the 100% prior-year harbor applies (the 110% tier starts at $150,000). This year she expects $90,000 of net freelance income.
Her current-year federal income tax is about $10,970— income-tax only, the engine's scope. Real self-employment income also carries self-employment tax (15.3% on most of it), which the engine does not model.
Her harbors: 90% of $10,970 is $9,873; 100% of last year's $9,610 is $9,610. The binding target is the prior-year harbor. With no paycheck to bump, she pays four quarterly estimates of $2,402.50 through Form 1040-ES or EFTPS. Pay all four and the harbor is cleared: she still owes $1,360 in April, but the penalty is zero.
Pay nothing all year and the whole $9,610 is short: at 7%, about $450 of penalty, plus the full $10,970 balance at filing. The prior-year harbor is cheap insurance when last year's number is small.
What a miss actually costs
The §6654 charge is interest, computed per quarter on each quarter's shortfall, at the federal short-term rate plus three points: 7% for early 2026, reset quarterly. A $10,000 shortfall spread evenly across the four quarters costs about $470. And if your balance due after withholding is under $1,000, there is no penalty at all, harbors or not (§6654(e)(1)).
The full mechanics, including the per-quarter timing math, are in the underpayment penalty guide →
When the IRS waives the penalty
Form 2210's instructions allow the penalty to be waived, in whole or in part, in two situations:
- Retirement or disability. You retired after reaching age 62, or became disabled, in the current or prior tax year, and the underpayment was due to reasonable cause rather than willful neglect.
- Casualty, disaster, or other unusual circumstance, where imposing the penalty would be inequitable.
Both require filing Form 2210 with a statement and documentation (retirement date and age, or police, insurance, or FEMA reports). In a federally declared disaster, the waiver is automatic for taxpayers in the covered area.
A waiver is mercy after the fact; a harbor is a rule you can plan around. The sections above are the planning route; keep Form 2210's waiver in reserve.
How to pay
- Raise your withholding (W-4 line 4c, "extra withholding"). Divide your remaining gap by your remaining paychecks and put that amount on a new W-4. Every dollar lands with the even-treatment benefit.
- Make quarterly payments (1040-ES or EFTPS). The right path with no wages — freelance income, investment income, retirement distributions. Form 1040-ES has the worksheet; EFTPS is the free online payment system.
- Mix them. High earners often hold the W-4 at the prior-year harbor and true up one quarter if a big vest or sale lands late.
One thing to pay attention to: the safe harbors are forgiving — pay 100% of last year's tax (110% above $150,000 AGI) or 90% of this year's, and the penalty goes away entirely.
FAQ
How much do I have to pay during the year to avoid the penalty?
The smaller of 90% of this year's total tax or 100% of last year's — 110% if last year's AGI was over $150,000. Pay it through withholding or quarterly estimated payments, and the underpayment penalty is zero no matter how large the April balance.
Is the 110% test based on this year's or last year's income?
Last year's. The AGI on last year's return sets the figure for this year's payments. A $180,000-AGI year means the next year's payments are figured against a 110% target.
Should I raise my W-4 withholding or make quarterly estimated payments?
If you have wages, the W-4. Withholding is treated as paid evenly across all four quarters no matter when it lands; estimated payments are credited to their own quarter only.
I cleared a safe harbor but still owe a lot in April. Is that a problem?
No. The harbor eliminates the penalty, not the tax. In the first vest year above, $16,403 was due at filing with a penalty of $0, because 110% of the prior year's tax was paid during the year. Pay the balance by the filing deadline and it ends there.
What does missing every safe harbor actually cost?
The underpayment penalty runs about 7% a year in early 2026, computed per quarter on each quarter's shortfall: a $10,000 shortfall spread evenly across the four quarters costs about $470.
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