Self-Employed Quarterly Tax Calculator
Calculate self-employed quarterly estimated tax payments per IRS Form 1040-ES. Combines federal income tax + self-employment tax (15.3% on net SE earnings, with deductions for half SE tax and qualified business income). Hits the safe-harbor rule (110% of prior year for AGI >$150K, 100% otherwise) to avoid underpayment penalty.
Why You Pay Quarterly
If you owe ≥$1,000 in tax after withholding, the IRS requires equal quarterly payments throughout the year (April 15, June 15, Sept 15, Jan 15 of following year). Failure triggers an underpayment penalty (current IRS rate 8%, compounded daily). Calculation uses Form 1040-ES. Self-employed face a double whammy: federal income tax PLUS 15.3% self-employment tax (12.4% Social Security up to $168,600 in 2024 + 2.9% Medicare, plus 0.9% Additional Medicare on wages above $200K/$250K MFJ).
Safe Harbor — Two Rules
You avoid the underpayment penalty if you pay AT LEAST: (1) 90% of current-year tax liability, OR (2) 100% of prior-year tax liability (110% if prior-year AGI exceeded $150,000 / $75K MFS). The 'prior year' safe harbor is the simpler — divide prior year tax by 4, pay each quarter. Higher earners must use 110%. Most self-employed use the prior-year rule because current-year income is variable.
Self-Employment Tax Deductions
Three big deductions reduce taxable SE income: (1) Half of SE tax deductible above-the-line on Schedule 1 (~7.65% effective reduction). (2) Qualified Business Income (QBI) deduction — 20% of QBI for pass-through businesses up to income threshold ($241,950 single / $483,900 MFJ for 2024). (3) Self-employed health-insurance premiums fully deductible above-the-line. Combined effect: net SE income is taxed roughly 25-30% lower than pure W-2 income for many self-employed.
Common Quarterly Tax Mistakes
(1) Forgetting state quarterly payments — most states with income tax require separate quarterlies. (2) Not adjusting after a big-income quarter — the safe harbor protects from penalty, but you'll owe a big April balance. (3) Missing the Sept 15 payment because Q3 covers June 1 - Aug 31 (not July 1 - Sept 30). (4) Forgetting estimated tax for one-time events (Roth conversion, large cap gain). (5) Not tracking estimated tax payments on Form 1040 line 26 at filing — IRS sometimes loses payments and assesses penalty without that documentation.
Sources: IRS Form 1040-ES Instructions 2026, IRC §6654 (estimated tax penalty), Rev. Proc. 2024-40 (inflation adjustments), Publication 505. Last updated: May 2026. Not tax advice.