Why equity years cause penalties
The US tax system is pay-as-you-go. If too little is paid during the year, the IRS charges an underpayment penalty, calculated like interest on each quarter's shortfall. Equity income often creates a shortfall because:
- RSU and NSO income is withheld at a flat 22%
- stock sales have no withholding
- ISO disqualifying income has no withholding
The safe-harbor rules
You owe no penalty if your total withholding plus estimated payments is at least the smaller of:
- 90% of this year's tax, or
- 100% of last year's tax, or 110% if last year's adjusted gross income was over $150,000 ($75,000 married filing separately).
You'll still owe the rest in April, but without a penalty.
Why last year's tax is powerful
In a windfall year, 90% of this year's tax can be huge. The prior-year option is a fixed, known number. Pay 110% of last year's total tax through withholding and estimates, and you're protected no matter how big this year gets.
2026 deadlines
- April 15, 2026: income from January through March
- June 15, 2026: April through May
- September 15, 2026: June through August
- January 15, 2027: September through December
The safe-harbor amount is normally paid in four equal installments.
Lumpy income: the annualized method
If your big income came late in the year, the annualized income installment method (Form 2210, Schedule AI) lets you match payments to when the income actually arrived. That can remove penalties for earlier quarters.
Withholding beats estimates
Withholding is treated as paid evenly through the year, whenever it actually happened. Increasing your W-4 withholding in November can cover a shortfall from April. Estimated payments only count from the date you make them.
State rules
Most states have similar safe harbors and deadlines, but not identical ones. California, for example, requires 30%, 40%, 0% and 30% of the year's estimate in its four installments, and doesn't allow the prior-year safe harbor for incomes of $1 million or more.
See your schedule
The calculator shows your estimated payment schedule and safe-harbor target for your scenario.
General information, not tax advice.
Frequently asked questions
What is the safe harbor rule for equity income taxes?
You avoid underpayment penalties if your total withholding and estimated tax payments equal at least 90% of your current year's tax liability. Alternatively, you can pay 100% of last year's total tax, or 110% if your previous adjusted gross income exceeded $150,000. This ensures you pay the remaining balance in April without facing extra penalties.
How do I avoid penalties if my income is much higher this year?
The prior-year tax rule is a powerful strategy because it uses a fixed, known amount from your previous return. By paying 110% of last year's total tax through withholding and quarterly estimates, you are fully protected from underpayment penalties regardless of how large your windfall becomes during the current year.
Can I use the annualized income method for tax payments?
If you received your large equity income late in the year, you may use the annualized income installment method. This allows you to match your tax payments to the specific periods when your income actually arrived. Using Form 2210 and Schedule AI can help you remove penalties for earlier quarters when your income was lower.
Is it better to pay estimated taxes or increase withholding?
Increasing your W-4 withholding is often superior because the IRS treats it as being paid evenly throughout the year. You can adjust your withholding as late as November to cover an earlier shortfall. Conversely, estimated payments only count toward your requirement starting from the specific date you actually make the payment.
Official sources (for the detail-minded)
- IRC Section 6654(d)(1)The 100% / 110% of last year's tax safe harbor
- IRC Section 6654(d)(2)The annualized income method for uneven income
- IRS Form 2210The form used to figure or avoid the underpayment penalty
- IRS Form 1040-ESHow to calculate and send estimated tax payments
- IRS Publication 505IRS guide to withholding and estimated tax
Run your own numbers
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Keep reading
Too Little Tax Taken Out? How to Spot and Fix Underwithholding
Your employer withholds a flat 22% on most equity income, but your real rate can be far higher. Here's how to spot the gap and close it.
Penalties for Paying Tax Late: Underpayment, Late-Payment and Late-Filing
Three different penalties can apply when tax is paid late. Here's what each costs and how the safe harbors keep you clear.
How commissions and bonuses are taxed and withheld
A commission check isn't taxed at a special rate, but it's withheld differently from your salary. Here's why big checks can look over-taxed, and why you may still owe in April.
How ESPP shares are taxed
Your ESPP discount is taxed when you sell, not when you buy. How much counts as salary depends on how long you held the shares.
Estimates only. Not tax, legal, or investment advice. See our methodology