How to file a tax extension, and what it does not cover
Pay online and mark it as an extension, e-file Form 4868, or mail it by the due date. You get six more months to file, not to pay. Steps, penalties, Illinois.
Prepared by Prem Tax and Accounting Corp. Last checked against official sources on October 24, 2026.
By the original due date, do one of three things: pay online and mark the payment as an extension payment, e-file Form 4868, or mail Form 4868. You get six more months to file, not to pay. Tax you owe is still due on the original date, and penalties and interest start from then on whatever remains unpaid.
- Form 4868 asks for an estimate: your tax for the year minus the tax you have already paid. E-filing asks for last year's AGI.
- The IRS says Free File's extension form has no income limit.
- Fiscal-year filers use the paper form. Businesses use Form 7004, which also gives six months.
- As of October 2026 the window for 2025 returns has closed. The next one is for 2026 returns, due April 15, 2027 by our calendar math.
Three ways to extend
Pay online and mark it
Use Direct Pay, your IRS online account, a card or digital wallet, or EFTPS, and choose the option that marks it as an extension payment.
E-file Form 4868
Use tax software or Free File. Have last year's AGI ready.
Mail Form 4868
Send the paper form so it is postmarked by the original due date.
What an extension does not change
| Item | Rule as of October 2026 |
|---|---|
| Late-filing penalty | 5% of the unpaid tax per month, up to 25%, trimmed by 0.5% in months the late-payment penalty also applies |
| Late-payment penalty | 0.5% of the unpaid tax per month, up to 25% |
| Interest | Federal short-term rate plus 3 points, reset each quarter and compounded daily. Check the IRS page for the current rate. |
Illinois has no extension form. The state gives an automatic six months to file, but any tax must be paid by April 15 with Form IL-505-I through MyTax Illinois, or penalty and interest run from the original date. See the Illinois Department of Revenue.
An example (invented)
Sam expects to owe about $3,000 and is waiting on a late tax form. Before the deadline he pays $3,000 online as an extension payment. That payment also serves as his extension request, so he has six more months to file. If his final bill is $3,400, penalties and interest apply only to the $400 shortfall.
What to bring or do next
- Your best estimate of the year's tax and what you have already paid.
- Last year's AGI, for e-filing.
- A list of the documents you are still waiting for.
- If you cannot pay in full, still file or extend by the due date, and ask us about your options.
Common questions
What if I cannot pay by the deadline?
File or extend on time anyway, because the late-filing penalty is larger than the late-payment penalty. Pay what you can. If you filed on time and have an approved payment plan, the late-payment rate drops to 0.25% a month.
How long is the extension?
Six months from the original due date. For a calendar-year individual return, that moves the filing date from April 15 to October 15.
Does an extension cover my state return?
Not automatically. Illinois gives six months to file but not to pay. Other states have their own rules, so check yours.
Do businesses use the same form?
No. Businesses use Form 7004, which also gives six months. For calendar-year filers that means September 15 for partnerships and S corporations, and October 15 for C corporations.
Official sources
- IRS: Get an extension to file your tax return
- IRS: Failure to file penalty
- IRS: Failure to pay penalty
- IRS: Interest rates remain the same for the fourth quarter of 2026
- Illinois Department of Revenue: Due dates and extensions
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