Definition
Extra time to file your federal return, usually to October 15, granted with Form 4868; it does not give extra time to pay.
What it means
Individuals can get an automatic six-month extension to file their federal return by submitting Form 4868 by the regular due date, or by paying all or part of the tax electronically and marking the payment as an extension. For most people, that moves the 2026 filing deadline from April 15, 2027 to October 15, 2027. An extension to file is not an extension to pay. Interest and the failure-to-pay penalty, generally 0.5% of unpaid tax per month, run from the April due date on any balance. The failure-to-file penalty, generally 5% of unpaid tax per month up to 25%, applies if you miss the extended deadline. U.S. citizens and residents living abroad get an automatic two-month extension. Disaster areas may receive extra time from the IRS.
Example
Someone who owes $2,000 and files Form 4868 but pays nothing until October could owe about $60 in failure-to-pay penalties (6 months x 0.5% x $2,000) plus interest.
Illustrative numbers only. Your situation will differ.