Definition
Quarterly tax payments people make on income that has no withholding, such as self-employment, rental or investment income.
What it means
The U.S. tax system is pay-as-you-go. If you expect to owe $1,000 or more when you file after subtracting withholding and refundable credits, you generally need to make estimated tax payments using Form 1040-ES. For tax year 2026, the due dates are April 15, June 15 and September 15, 2026, and January 15, 2027. You can avoid an underpayment penalty if your withholding and estimated payments cover at least 90% of this year's tax or 100% of last year's tax, or 110% if last year's AGI was over $150,000. Payments can be made online through IRS Direct Pay or your IRS online account. Employees with side income can instead raise W-4 withholding at their main job. Most states have their own estimated tax rules.
Example
A freelancer who expects to owe $8,000 for 2026 could pay $2,000 on each of the four due dates. If last year's tax was $6,000 and AGI was under $150,000, paying $1,500 each quarter meets the safe harbor.
Illustrative numbers only. Your situation will differ.