Quarterly estimated tax guides

Everything the calculator does, explained: how the IRS decides what you owe each quarter, when it is due, and what happens if you get it wrong. Written for freelancers, investors and anyone whose income does not arrive in four equal pieces.

• IRS Form 2210 Schedule AI: the Annualized Income Installment Method explained

  What Form 2210 Schedule AI does, who should use the annualized income installment method, and how the four annualization periods and 22.5% / 45% / 67.5% / 90% installment thresholds work.

• Estimated tax safe harbor rules: the 90%, 100% and 110% tests

  The two estimated tax safe harbors — 90% of this year’s tax, or 100% of last year’s (110% if your prior-year AGI was over $150,000) — and which one costs you less.

• Quarterly estimated tax due dates for 2024, 2025 and 2026

  Every quarterly estimated tax payment deadline for the 2024, 2025 and 2026 tax years, including the weekend and holiday shifts, plus the income period each payment covers.

• The IRS estimated tax underpayment penalty: how it is calculated

  How the underpayment penalty is charged quarter by quarter at the IRS interest rate, the $1,000 de minimis exception, and the ways to reduce or remove it on Form 2210.

• Self-employment tax and quarterly estimated payments

  How the 15.3% self-employment tax works for freelancers and 1099 contractors, the Social Security wage base, the 92.35% net earnings factor, and how it feeds your quarterly estimates.

• Estimated taxes on capital gains, RSUs and other lumpy income

  What to pay, and when, after a large stock sale or RSU vest — long-term capital gains rates, the 3.8% Net Investment Income Tax, and why annualizing usually beats equal installments.

Ready to run the numbers? Open the free estimated tax calculator.