Quarterly Estimated Tax Calculator

This quarterly estimated tax calculator answers one specific question: how much do you need to send the IRS four times a year to avoid an underpayment penalty? It projects your self-employment tax and federal income tax for the year, then applies the IRS safe-harbor rule from Form 1040-ES — pay the smaller of 90% of this year's tax or 100% (110% if your prior-year AGI exceeded $150,000) of last year's tax — and splits the required amount into four equal installments.

Worked example (the defaults): $80,000 in projected net self-employment profit, $2,000 already withheld from other income, and $12,000 in total tax owed last year. Projected self-employment tax is $11,303.64, projected federal income tax is $7,526.60, for a current-year total of $18,830.24. Ninety percent of that is $16,947.22 — but since last year's tax of $12,000 is smaller, that becomes the safe-harbor target. After subtracting the $2,000 already withheld, you need to pay in $10,000 across the year — $2,500 per quarter.

Want the full breakdown of how the self-employment tax portion itself is calculated — including the 92.35% net earnings factor and the Social Security wage base cap? See the Self-Employment Tax Calculator.

The IRS doesn't require you to predict your income perfectly. It requires you to pay in enough across the year — through withholding, estimated payments, or both — to avoid an underpayment penalty. Form 1040-ES sets that bar as the smaller of two numbers:

This is why the calculator asks for last year's total tax liability (Form 1040, Line 22): if your income is growing, the prior-year figure is usually the lower — and easier to hit — target, since it's a known number rather than a projection. If you leave the prior-year field at zero, the calculator falls back to the 90%-of-current-year target only, which is the more conservative (typically higher) number.

Missing the safe-harbor target doesn't always mean a penalty — the IRS calculates the actual underpayment penalty based on how much you were short in each period, using published interest rates. But paying at least the safe-harbor amount, spread evenly across the four due dates, is what guarantees no penalty regardless of how your income actually lands.

Despite the name, the four "quarters" aren't equal in length — they follow a set schedule from the IRS Form 1040-ES instructions:

• Q1: April 15 — covers income from January through March
• Q2: June 15 — covers April and May (a short quarter)
• Q3: September 15 — covers June through August
• Q4: January 15 (following year) — covers September through December

If any due date falls on a weekend or federal holiday, it shifts to the next business day. Payments can be made online through IRS Direct Pay, the Electronic Federal Tax Payment System (EFTPS), or by mailing a check with the payment voucher from Form 1040-ES. If your income is uneven across the year — common for seasonal freelance or contract work — the IRS also allows the annualized income installment method, which lets you pay less in slow quarters and more in high-earning ones instead of four flat payments; that method isn't modeled here since it requires quarter-by-quarter income detail, but the flat quarterly figure above is a safe, simple default for most self-employed filers.