Safe Harbor Tax Rules: 110% Threshold, Prior-Year Target, and Waivers

The safe harbor rules for estimated taxes let you avoid the IRS underpayment penalty by paying, through withholding and quarterly installments, either 90% of your current-year tax or 100% of your prior-year tax. If your prior-year adjusted gross income was over $150,000, that second figure rises to 110%. Hit either target and the penalty doesn’t apply, even if you still owe a large balance when you file.

The Two Thresholds

You have two ways to stay penalty-free, and you only need to satisfy one. The IRS checks both and applies whichever produces the smaller required payment.

Current-year method. Your total payments (estimated taxes plus any withholding) equal at least 90% of the tax shown on your current-year return.
Prior-year method. Your total payments equal at least 100% of the tax shown on last year’s return.¹

Most people lean on the prior-year method because the number is already known. Pull the “total tax” line from last year’s Form 1040 and that’s your target. No forecasting.

The 90% current-year method has no income-based adjustment. Whether you earn $60,000 or $6 million, covering 90% of your current-year liability keeps you penalty-free. That can be the cheaper route in years when income drops sharply from the prior year.

The 110% Rule for Higher Incomes

If your adjusted gross income on last year’s return exceeded $150,000 ($75,000 if married filing separately), the prior-year safe harbor jumps to 110% of your prior-year tax.² The 90% current-year option is unchanged at higher incomes.

If You Owed Nothing Last Year

If your prior-year return showed zero total tax, or you weren’t required to file, you’re exempt from the estimated tax penalty entirely for the current year. Two conditions apply: the prior year must have been a full 12-month tax year, and you must have been a U.S. citizen or resident the whole time.¹ The exemption covers only the penalty. You still owe the actual tax when you file.

Working the Prior-Year Target

Take the “total tax” line from your most recent Form 1040. If your 2025 AGI was $150,000 or less, that figure is your 2026 safe harbor target. If your 2025 AGI was over $150,000, multiply by 1.10.

Say your 2025 total tax was $40,000 and your AGI was $120,000. Your 2026 target is $40,000. If your 2025 AGI was $200,000 instead, the target becomes $44,000. Divide the target into four equal installments.¹

The appeal is certainty. If your income jumps in 2026, you may owe a large balance when you file, but you won’t owe a penalty on top of it, as long as your payments hit the prior-year figure. Owing tax and owing a penalty are not the same thing, and confusing the two costs people money every year.

2026 Payment Due Dates

The tax year splits into four unequal income periods, each with its own deadline:³

First installment (income from Jan 1 through Mar 31): April 15, 2026
Second installment (Apr 1 through May 31): June 15, 2026
Third installment (Jun 1 through Aug 31): September 15, 2026
Fourth installment (Sep 1 through Dec 31): January 15, 2027

When a due date falls on a weekend or legal holiday, it shifts to the next business day. All four 2026 dates land on weekdays with no holiday conflicts.⁴ You can skip the January 15, 2027 payment if you file your 2026 return and pay the full remaining balance by February 1, 2027.³

You submit payments using Form 1040-ES vouchers, IRS Direct Pay, EFTPS, or a credit or debit card through a third-party processor.⁵

Withholding Counts, and It Counts Evenly

If you also have W-2 wages or other income subject to withholding, those withheld amounts count toward your safe harbor target. The IRS treats one-fourth of your annual withholding as paid on each quarterly due date, regardless of when it was actually withheld.⁶

That’s useful. A large December withholding hit effectively gets spread across all four quarters for penalty purposes. If you realize in October that you’re behind, boosting your W-2 withholding for the rest of the year can retroactively fix earlier quarters in a way that a fourth-quarter estimated payment cannot. You can override the equal-split default and allocate withholding to the actual dates it was taken, but the default usually works in your favor.

When Your Income Isn’t Steady: Annualized Income

Equal quarterly payments work fine for steady income. They don’t work well for a seasonal business, a one-time consulting contract in October, or a fourth-quarter stock sale. Paying one-fourth of your annual target by April 15 when you’ve barely earned anything is a real cash flow problem.

The annualized income installment method ties each quarter’s required payment to the income you’ve actually earned through that point. Earned nothing in the first three months? Your first required installment can be zero. The IRS applies escalating percentages to your annualized income at each due date: 22.5% for the first period, 45% for the second, 67.5% for the third, and 90% for the fourth.¹

The catch: any reduction in an early quarter is recaptured in later installments. If your first required installment drops from $5,000 to $0, that $5,000 shifts into the following quarters. You’re deferring, not eliminating.

You claim this method by completing Schedule AI of Form 2210 and checking box C in Part II. The calculation requires you to figure taxable income, self-employment income, and deductions for each sub-period, so you need solid records of when income arrived and when expenses were paid.⁷

If You Miss the Safe Harbor

Miss every threshold and the IRS charges an underpayment penalty that functions like interest on the shortfall. The rate is the federal short-term rate plus three percentage points, recalculated quarterly. For the first quarter of 2026 the individual underpayment rate is 7%. For the second quarter it drops to 6%.⁸⁹

The penalty is calculated separately for each installment period. A shortfall on the April 15 installment starts accruing immediately and keeps running until you make up the difference or reach your return’s due date, whichever comes first. A missed early-year quarter builds up more penalty than a missed fourth-quarter payment because the clock runs longer.¹⁰

The IRS usually figures the penalty for you from the information on your return. You only need to file Form 2210 if a special situation applies or you’re using the annualized income method.¹¹

The $1,000 Floor

Even if you miss the safe harbor, no penalty applies if your total tax minus withholding and refundable credits is less than $1,000. This is a separate escape hatch, not part of the safe harbor calculation.¹

Waivers

The IRS can waive the underpayment penalty in narrow circumstances:

You retired after reaching age 62 or became disabled during the tax year or the year before, and the underpayment resulted from reasonable cause rather than neglect.¹
A casualty, federally declared disaster, or other unusual circumstance made imposing the penalty inequitable. For federally declared disasters the IRS applies relief automatically. Otherwise, you request the waiver by checking box B on Form 2210 with a written explanation and supporting documentation.⁷

“I didn’t realize I needed to make estimated payments” and “my accountant forgot” don’t qualify. And note: the IRS’s First Time Abate program, which forgives certain penalties for taxpayers with a clean history, does not apply to the estimated tax underpayment penalty. First Time Abate covers failure-to-file and failure-to-pay penalties only.¹²

Boundaries to Know

Farmers and fishermen. If at least two-thirds of your gross income comes from farming or fishing, different rules apply. You make a single estimated payment by January 15 of the following year, and the required amount is two-thirds (66⅔%) of your current-year tax rather than 90%. You can also skip estimated payments entirely by filing and paying in full by March 1. The 110% high-income surcharge does not apply here.¹¹³

State taxes. Most states with an income tax have their own estimated tax rules, and they don’t always mirror the federal ones. Some states set safe harbor at 90% of current-year liability with no prior-year alternative. Meeting the federal safe harbor does not automatically protect you at the state level, so check your state tax agency separately.

1
Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual To Pay Estimated Income Tax
2
Internal Revenue Service. Underpayment of Estimated Tax by Individuals Penalty
3
Internal Revenue Service. Form 1040-ES (2026)
4
Internal Revenue Service. Publication 509 (2026), Tax Calendars
5
Internal Revenue Service. About Form 1040-ES, Estimated Tax for Individuals
6
Internal Revenue Service. Publication 505 (2025), Tax Withholding and Estimated Tax
7
Internal Revenue Service. Instructions for Form 2210 (2025)
8
Internal Revenue Service. Interest Rates Remain the Same for the First Quarter of 2026
9
Internal Revenue Service. Internal Revenue Bulletin 2026-8
10
Internal Revenue Service. Quarterly Interest Rates
11
Internal Revenue Service. Form 2210 Underpayment of Estimated Tax by Individuals, Estates, and Trusts
12
Internal Revenue Service. Administrative Penalty Relief
13
Internal Revenue Service. Farming and Fishing Income