Free tool
Quarterly estimated tax calculator.
IRS safe-harbor, 2026 brackets.
The IRS expects self-employed taxpayers to pay tax quarterly. Underpaying triggers the underpayment penalty. The safe-harbor rule lets you avoid that penalty entirely by paying the lower of two known amounts. This tool computes both.
Estimate only. The IRS safe-harbor rule lets you avoid the underpayment penalty by paying the lower of (a) 100% of prior year’s total tax, or (b) 90% of current year’s actual tax. Quarterly due dates are typically April 15, June 15, September 15, and January 15 of the following year. Talk to a CPA before relying on these numbers for actual payments.
How safe-harbor works
Two ways to avoid the underpayment penalty.
IRS Form 1040-ES gives you two safe-harbor options. Pay the LOWER of the two and you’re penalty-proof for the year, regardless of how much your actual income spikes.
- Prior-year method. Pay 100% of last year’s total tax (110% if your prior-year AGI was above $150,000 for single or married-filing-jointly, or $75,000 for married-filing-separately). This number is fixed once your prior year is filed — the cleanest path for vendors with irregular income.
- Current-year method. Pay 90% of this year’s actual tax. This is harder to pin down because you don’t know your full-year income until December. The calculator projects from your year-to-date income.
- Quarterly due dates. April 15, June 15, September 15 (of the current year), and January 15 (of the next year). Late payments accrue the underpayment penalty even if you pay the full annual amount by year end.
- What counts as “tax” for safe-harbor. Self-employment tax + federal income tax + state income tax + any additional Medicare tax. Sales tax and property tax are not part of the calculation.
Stop guessing at quarterly payments.
BookNox helps service vendors close inquiries on the spot — quote, sign, deposit, all in one link. More consistent income means more accurate quarterly projections.