TaxStache 2026–2027 Quarterly Tax Calendar and Estimated Payment Worksheet

This worksheet exists because estimated taxes have a calendar problem. The deadlines aren't evenly spaced, the "quarters" aren't actually quarters, and the IRS does not send reminders. Most small-business owners know they're supposed to pay estimated taxes. The part that trips them up is when, how much, and what happens when they guess wrong.

The system itself is not complicated. There are four dates, two calculation methods, and one penalty to avoid. This worksheet walks through all three so you can pick the right method, pay the right amount, and stop treating quarterly taxes like a pop quiz you forgot to study for.

Important reminder: The IRS charges an underpayment penalty per quarter, not annually. Catching up in Q4 does not erase a missed Q2 payment. Each quarter's penalty runs from its own deadline until you pay or until April 15 of the following year, whichever comes first. The penalty rate has been running 7% to 8% annualized, which is real money on a real balance.