Filing an extension: what it buys you, and the payment it doesn’t delay

What an extension actually does

An extension gives you more time to file a complete, accurate return. For individuals, Form 4868 moves the filing deadline for a 2025 return from April 15, 2026 to October 15, 2026. Businesses use Form 7004, which generally provides an automatic six-month extension for partnerships, S corporations and C corporations.

The extension is automatic. You don’t give a reason, and the IRS doesn’t approve or deny it as long as it’s filed by the original due date.

For many business owners and high earners, extending is simply practical. K-1s from partnerships and funds often arrive late, and filing before they do can mean amending later.

The deadlines that apply to you

• Individuals (Form 1040): due April 15; extended to October 15
• Partnerships (Form 1065) and S corporations (Form 1120-S), calendar year: due March 15; extended to September 15
• C corporations (Form 1120), calendar year: due April 15; extended to October 15. C corporations with a June 30 year-end get a seven-month extension instead of six.
• US citizens and residents living abroad: an automatic two extra months to file and pay, to June 15, with interest still running from April 15. Filing Form 4868 adds four more months.
• Weekends and holidays push a deadline to the next business day; disaster declarations can postpone deadlines for affected areas

What it doesn’t do

An extension of time to file is not an extension of time to pay. Your tax is still due by the original deadline, and the business extension on Form 7004 works the same way.

Interest accrues on any unpaid balance from the original due date until it’s paid. The rate resets quarterly; for individuals it is 7% a year, compounded daily, for the fourth quarter of 2026. A failure-to-pay penalty of 0.5% of the unpaid tax per month, up to 25%, can apply as well.

There’s a useful safe harbor. If at least 90% of your actual tax is paid by the original due date — through withholding, estimated payments or a payment with the extension — and you pay the rest with a return filed by the extended deadline, the IRS treats you as having reasonable cause and the failure-to-pay penalty doesn’t apply for the extension period. Interest still does.

What the penalties really cost: an example

Suppose your 2025 tax is $20,000 and you paid $15,000 by April 15, leaving $5,000 unpaid. You file and pay the balance on October 1.

With an extension, you owe a failure-to-pay penalty of 0.5% for six months (a partial month counts as a full one), or $150, plus roughly $160 of interest at a 7% annual rate. The 90% safe harbor doesn’t help here because you paid only 75%.

Without an extension, the failure-to-file penalty applies too: 5% a month, reduced by the failure-to-pay penalty for the same month, capped after five months. That adds about $1,125, for a total near $1,435 instead of $310. Returns more than 60 days late also face a minimum penalty — $525 or 100% of the tax due, whichever is less, for returns due after December 31, 2025.

• Lesson one: always file the extension, even if you can’t pay
• Lesson two: pay at least 90% by April and the failure-to-pay penalty generally disappears

What to gather before you extend

An extension is only as good as the estimate behind it. A few hours in early April can prevent months of interest and a penalty that the 90% rule would have avoided.

• Your prior-year return, for a baseline and to check the safe harbor you used for estimates
• Year-to-date profit and loss and balance sheet for each business, closed through December
• W-2s, 1099s and any K-1s that have arrived; for missing K-1s, an estimate from the partnership or last year’s figures adjusted for known changes
• A record of every estimated payment made for the year, including any overpayment applied from the prior year
• Large one-time items: property or stock sales, a business sale, retirement distributions, Roth conversions
• State information: which states you earned income in and whether each requires its own extension form or payment

How to extend well

• Estimate your tax before the April deadline using your best available numbers — last year’s return, year-to-date books, and any K-1 estimates you can get
• Pay what you expect to owe, ideally at least 90%, with the extension
• If you pay electronically through Direct Pay, EFTPS, or a card and designate the payment as an extension payment, the IRS treats that as your extension request; no separate Form 4868 is needed
• Keep the confirmation number with your records
• Report the extension payment on your return (Schedule 3 of Form 1040) so it’s credited
• Don’t forget first-quarter estimates for the new year, which are due the same April day

If October 15 is getting close

There’s generally no second federal extension for individuals living in the US. If your return isn’t done, the priority is to file a complete and accurate return by the deadline, even if a few items are still estimates — you can amend later if a corrected K-1 arrives.

If you can’t pay the balance, file on time anyway and pay what you can. A payment plan reduces the failure-to-pay rate to 0.25% a month while it’s in effect.

If a penalty has already been charged and you have a clean record for the prior three years, the IRS’s first-time abatement policy can remove failure-to-file and failure-to-pay penalties; interest tied to the removed penalty is reduced too. You request it by phone or on Form 843.

What an extension changes elsewhere

• SEP-IRA contributions and Solo 401(k) employer contributions can generally be made up to the extended due date, but only if you actually extended
• Traditional and Roth IRA and HSA contributions for the prior year are still due by the original April deadline
• The three-year period the IRS has to assess additional tax generally starts when you actually file, so an extended return’s clock starts later
• An extension doesn’t extend the time to make most elections that are due with a timely filed return unless the election rules say so; check any you’re planning
• States set their own rules. Many accept the federal extension automatically, some require their own form, and nearly all still require payment by the original date

Common mistakes

Because extension payments, estimates and retirement contributions all interact, it helps to have a preparer build the April estimate and confirm what to pay. At Tally Tax, extended returns are tracked against both the federal and state deadlines so nothing slips into late-filing territory.

• Extending without paying, then being surprised by interest and penalties that ran from April
• Filing the extension for the wrong year or with the wrong Social Security number on an electronic payment
• Missing the September 15 deadline for an extended partnership or S corp return, which delays every owner’s personal return and can trigger per-partner or per-shareholder late-filing penalties
• Treating October 15 as flexible; it isn’t

Frequently asked questions