The four dates that rule freelance cash flow
Estimated tax for 2026 income is due April 15, June 15, September 15 and January 15, 2027 — deliberately uneven quarters (the first "quarter" is four months, the second two) that catch new freelancers out every year. Payment is for income already earned in that period, not a flat subscription: a $40,000 project landing in May belongs mostly to the June 15 payment. The calculator splits your projected annual tax into four equal installments by default — simple and penalty-safe — and the text below explains when uneven splitting is worth the tracking effort.
What goes into the "annual tax" you are splitting
For self-employment income the number is bigger than income tax alone: it includes the 15.3% self-employment tax computed on 92.35% of net profit up to the 2026 Social Security ceiling of $184,500. The engine also credits the half-SE deduction and your standard deduction before running the 2026 brackets, so the quarterly figure is the true combined obligation — income tax and SE tax together, minus anything your day-job withholding already covers. If you entered wages in the withholding field, each quarterly payment drops by that share; zero-wage users see the full amount, which is the correct number to schedule.
The two safe harbors — pick one, forget worry
Penalties apply only when you underpay relative to a legal floor. Safe harbor one: pay 90% of the current year’s total tax through withholding plus estimates. Safe harbor two: pay 100% of last year’s total tax (110% if your prior-year income exceeded $150,000) in four equal installments, no matter how much you earn this year. Harbor two is the freelancer’s favorite: land a monster contract in November and you still owe nothing extra until filing — the IRS charges no penalty for growth, only for underpayment below the floor. The calculator evaluates both harbors against your inputs and labels which one you are currently meeting.
A worked example: $36,000 side profit, W-2 job covers withholding
Net profit $36,000 → SE tax ≈ $5,087. After the half-SE deduction ($2,543) and $16,100 standard deduction, taxable income on the profit alone is about $17,357 → income tax ≈ $1,842. Combined 2026 obligation ≈ $6,929; your W-2 withholding is entered as $0 (it covers only your salary, which has none of this profit). Four equal payments: $1,732 each — April 15, June 15, September 15, and January 15. Under-paid first quarter? The penalty computation is per-quarter, so catching up by June limits the damage to roughly the rate-plus-three-points on one quarter’s gap for three months — small, but why pay it at all when a calendar reminder is free.
Fixing withholding instead of paying estimates
If you also have W-2 wages, there is a trick: withholding is treated as paid evenly through the year regardless of when it actually happens, so asking payroll to extra-withhold (W-4 line 4(c)) in November can retroactively "cover" the March windfall — something a quarterly payment in January cannot do. The general rule of thumb: stable freelance income → quarterly estimates; volatile income with a salaried anchor → crank up withholding late in the year. Both routes reach the same safe harbor; choose by which mistake you are more likely to make, a missed date or a forgotten payroll form.
Estimates for planning only — not tax, legal or accounting advice. Your actual return depends on facts this tool does not ask about. Figures are based on IRS Revenue Procedure 2025-32 (tax year 2026), verified October 2026.