2026 Estimated Tax Due Dates

Missing the Q3 installment can cost you even if you catch up later. The underpayment penalty (Form 2210) is figured installment by installment: each quarter's required payment is compared with what you had paid by that quarter's own due date, so a short Q3 is penalised even if a later payment brings the year's total up to a safe harbor (the smaller of 90% of your current-year tax or 100% of your prior-year tax, 110% if your prior-year AGI exceeded $150,000, or $75,000 married filing separately). The addition to tax runs at the IRS underpayment rate (see current IRS interest rates) from the day the third installment was due, and stops on whichever comes first: the date that part of the shortfall is paid, or April 15, 2027, the 15th day of the fourth month after the tax year closes. After that, any balance still owing is charged ordinary interest. Check your exposure with the estimated tax penalty calculator, then catch up through the quarterly estimated tax calculator.

October 15 is a different deadline — it's the extended filing deadline for last year's return (Form 4868), not an estimated-tax due date. It never moved the payment deadline, which stayed at April 15. If your extended return still isn't filed after October 15, the failure-to-file penalty (5% of unpaid tax per month, capped at 25%; if the return is more than 60 days late, at least the smaller of $525 or the full tax due) starts running from October 16. In any month the failure-to-pay penalty (0.5%/month) also applies, the failure-to-file penalty is reduced by it (to 4.5%); interest keeps accruing from April 15. Estimate the total with the late filing penalty calculator.