Tax Calculator
Estimated Tax Safe Harbor
Know exactly how much to pay quarterly to avoid IRS underpayment penalties — using the safe harbor rules from your prior year tax return.
100% Safe Harbor Rule
Pay at least 100% of last year's total tax liability in estimated payments. Works for most filers.
110% Rule (High Earners)
If your prior year AGI exceeded $150,000 (single or MFJ), you must pay 110% of prior year tax to qualify for safe harbor.
Line 24 on your prior year Form 1040 — your total federal tax, not what you owed or refunded.
Line 11 on your prior year Form 1040. Used to determine if the 110% rule applies.
Federal income tax already withheld from any W-2 jobs this year. Reduces the amount you need to pay quarterly.
Based on IRS safe harbor rules under IRC §6654. Does not account for current-year income changes or alternative annualized method.
Assumptions (2026): Estimates use 2026 federal rates published by the IRS in Rev. Proc. 2025-32: standard deduction $16,100 single / $32,200 joint, Social Security wage base $184,500, self-employment tax 15.3% (12.4% Social Security + 2.9% Medicare). Figures do not include state tax, AMT, the additional 0.9% Medicare surtax, or the qualified business income deduction.
Safe harbor is computed from your prior-year return, so the result does not depend on 2026 brackets. Quarterly due dates shown are the 2026 tax-year dates (Q4 falls on January 15, 2027).
Figures last reviewed September 2026.