How quarterly estimated taxes work
A plain-English guide to why self-employed workers make four payments instead of one April payment.
What estimated tax covers
Estimated tax covers income tax and other taxes that are not prepaid through withholding. For a self-employed worker, that usually means federal income tax plus self-employment tax for Social Security and Medicare.
The practical goal is not to predict April perfectly. It is to prepay enough during the year that the IRS does not treat you as materially underpaid.
The four payment periods
The IRS uses four uneven payment periods: January through March, April through May, June through August, and September through December. That is why the second period is shorter than a normal calendar quarter.
The calculator stores those due dates in the tax-year rate table and splits the remaining estimate across the payment windows still open as of today's date.
How withholding and estimated payments work together
Withholding from W-2 work counts toward the same annual tax obligation as estimated payments. If you have both a job and 1099 income, your withholding can reduce or even eliminate the next estimated payment.
Enter federal withholding and estimated payments already made so the result panel can show the balance still uncovered.
The guide explains the rule. The calculator shows how it changes your next quarterly payment.
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