Quarterly Estimated Taxes: A Simple System That Works

Pay in either 100% of last year's total tax (110% if prior-year AGI was over $150K) or 90% of this year's tax, whichever is lower. Hit that across four equal quarterly payments and the IRS will not charge an underpayment penalty, even if you owe a balance at filing.

Take last year's tax, divide by four, and set those amounts aside automatically on January 1, April 1, June 1, and September 1. Park the cash in a high-yield savings account so the float earns something.

In November, re-forecast based on actual year-to-date income and adjust the January payment up or down.

Businesses with uneven income (tax preparers, retailers, contractors with summer seasons) can use Form 2210's annualized income installment method to align payments to when income is actually earned, instead of paying four equal amounts.

This requires solid monthly bookkeeping. Without good books, stick with safe harbor.

Georgia and most states run their own safe-harbor rules in parallel. A federal-only estimate plan leaves the state side exposed to interest and penalties.

Missing the January 15 Q4 deadline — it triggers a partial penalty even if the rest were on time. Skipping a payment because cash was tight, instead of paying late and capping the penalty. Letting withholding through a W-2 spouse cover both incomes without modeling whether it actually does.