Quarterly estimated taxes are the part of self-employment nobody explains well. The IRS periods are not even quarters, the amount depends on profit you have not finished earning, and the usual advice is "set aside 25-30%" with no way to check it. I built a spreadsheet (Excel + Google Sheets, no macros) that works it out from what you log. Here are the formulas.

The IRS periods are not quarters

Estimated tax "quarters" are Jan 1-Mar 31, Apr 1-May 31, Jun 1-Aug 31 and Sep 1-Dec 31, due Apr 15, Jun 15, Sep 15 and Jan 15 of the next year. Two months, three months, three months, four months. So each column on the Quarterly Tax tab builds its own start and end date from the tax year on Setup:

Start: =DATE(Setup!$C$7, 4, 1) End: =DATE(Setup!$C$7, 5, 31) Due: =DATE(Setup!$C$7, 6, 15)

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Q4's due date is DATE(year+1, 1, 15) .…