Quarterly estimated tax and the safe harbor rules
Self-employment income has no withholding, so the IRS expects tax paid quarterly through the year rather than in one lump sum the following April. Underpay by too much and you owe a penalty, regardless of whether you pay in full by the filing deadline. The safe harbor rules set the floor that avoids it.
Open the Quarterly Estimated Tax Calculator calculatorIf you expect to owe at least $1,000 in tax for the year after subtracting withholding, the IRS expects you to pay estimated tax in four instalments rather than all at once when you file. Missing this is not just a cash-flow problem, it can trigger an underpayment penalty even if you pay everything owed in full by the April filing deadline.
The three safe harbors
You avoid the underpayment penalty if your payments through the year meet any one of three tests, whichever is lowest:
- 90% of this year's tax, once it is finally known, which is of limited use in advance since you rarely know your final tax with precision mid-year.
- 100% of last year's tax, if your prior-year adjusted gross income was $150,000or less. This is the one most people rely on, since last year's tax is a known, fixed number as soon as that return is filed.
- 110% of last year's tax, if your prior-year AGI was above $150,000. Higher earners need to pay a slightly larger share of last year's bill to be protected.
Whichever of these produces the lowest required payment is the one that applies, so a prior-year safe harbor is usually the more useful anchor to plan around, precisely because it is a fixed, already-known number rather than a moving target based on income you have not finished earning yet.
No prior-year return
If you did not file a full 12-month return the previous year, for example your first year self-employed, the prior-year safe harbors are unavailable and only the current-year 90% test applies. This is the one case where you genuinely need to estimate this year's tax as you go.
The due dates
| Quarter | Due date |
|---|---|
| Q1 | 2026-04-15 |
| Q2 | 2026-06-15 |
| Q3 | 2026-09-15 |
| Q4 | 2027-01-15 |
These shift to the next business day whenever the standard 15th falls on a weekend or federal holiday, so always confirm the exact date for the current year rather than assuming the 15th.
How the OBBBA deductions change the number
The four Schedule 1-A deductions, tips, overtime, car loan interest and the senior deduction, reduce your projected total tax for the year, which in turn reduces your required quarterly payment under the current-year safe harbor. They do not change last year's tax, so they have no effect on a prior-year safe harbor calculation. If you expect to qualify for a meaningful Schedule 1-A deduction this year and are relying on the current-year 90% test, factor it in, overpaying quarterly estimated tax ties up cash you did not need to send the IRS until filing.
Next steps
Enter your expected income, prior-year tax and AGI, and expected withholding into the Quarterly Estimated Tax Calculator to see which safe harbor applies to you and what each of the four payments should be.