Free · US federal · tax year 2026
Quarterly Estimated Tax Guide
The rule, the four dates, and one worked example — every claim cited to an IRS form or the IRS Code.
What is in it
- Whether you owe estimated tax at all — and why that test is not the one that decides penalties
- The four due dates, and when the last one can be skipped
- The safe harbor, worked end to end with real numbers
- Four things you are allowed to do that most people never learn
- What the penalty actually is, and why no honest guide prints a rate for it
It explains the rule and works one example. It does not compute your number — that is what the Quarterly Tax Estimator is for. Everything in it is federal; your state, and sometimes your city, is a separate bill with separate rules.