I Filed an Extension — Now What? (October 15, 2026 Deadline)

The cost-of-waiting math

Worked example, computed live by the same engine that powers the IRS Penalty Calculator. Assume you owe $5,000 on your 2025 return, paid less than 90% of your total 2025 tax by April 15, filed Form 4868 on time, and file + pay on October 1, 2026 with no installment agreement:

• Failure-to-pay penalty: $150.00 (6 months × 0.50%)
• Interest: $153.81 (accrued at the quarterly IRS underpayment rate from April 15 through October 1)
• Failure-to-file penalty: $0.00 — the extension keeps this at zero as long as you file by Oct 15.
• Total owed: $5,303.81

The takeaway: on a $5,000 balance, waiting from April to October costs roughly $303.81 in penalty + interest. Every month you wait after paying is another ~0.50% plus interest — you can stop the bleeding today without filing by making a payment at IRS Direct Pay.

File even if you can't pay

This is the single most important sentence on the page: not filing costs 4.5% a month on top of the 0.5% late-payment penalty (9×). Miss October 15 and the 5.0%/month FTF penalty (capped at 25.0%) starts; in months when both apply, the IRS reduces it by the 0.5% FTP, so the two together cost 5% a month, plus the interest that is already running. And if the return ends up more than 60 days late, the minimum failure-to-file penalty applies — the lesser of the unpaid tax or $525.00 for returns due in 2026 (Rev. Proc. 2025-32 §3.42).

Bottom line: file on time even if you send $0. Then use an IRS short-term (up to 180 days) or long-term installment agreement — a long-term plan cuts the FTP in half while it's in effect.

Document checklist

• All W-2s and 1099s (NEC, MISC, K, INT, DIV, R, B, SA).
• Prior-year AGI from your 2024 return — required for e-file identity verification.
• Your IRS Identity Protection PIN (IP PIN), if you have one.
• 1098 forms — mortgage interest, student loan interest, tuition (1098-T for education credits).
• Records for the OBBB deductions. Tips: your 2025 W-2 box 7 (tips you reported to your employer), Forms 4070, or an employer statement. Qualified overtime: any amount your employer reported in box 14 or a separate statement, otherwise your pay stubs. (Box 12 code TP for tips and code TT for overtime start with 2026 W-2s.) Details in the OBBB W-2 reporting guide.
• Basis records for any brokerage 1099-B (especially crypto and RSU sales).
• Bank/routing numbers for refund direct-deposit or Direct Pay.

State deadlines vary

Many states honor the federal extension for the filing date but wanted the payment on April 15 — meaning state penalties and interest are already accruing on any state balance. A handful of states require a separate state extension form. Check your state's rules in the state tax guide before Oct 15.

Penalty relief: AEP (automatic) and First-Time Abate

If this ends up being your first slip after a clean three-year compliance history, the IRS's Automatic Exemption from Penalty (AEP) should apply when your 2025 return is processed: AEP covers eligible original returns beginning with tax year 2025, so the failure-to-file and failure-to-pay penalties shouldn't be assessed (interest always stays). If a penalty notice arrives anyway during the 2026 phase-in, ask for First-Time Abate — the fallback until AEP fully replaces it for returns due on or after January 1, 2027. See the IRS automatic penalty relief guide for eligibility and the exact request script.