By Charles Trautman, EA, IRS Enrolled Agent · September 18, 2026 · Last reviewed September 18, 2026

Tax extension deadline: October 15, 2026, for federal and Colorado returns

The extended tax deadline for 2025 individual returns is Thursday, October 15, 2026, for both the IRS and Colorado. The extension only moved the filing date. Tax you still owe has collected interest since April 15, and a late-payment penalty applies too unless you paid at least 90 percent by then.

Most people remember the date. What catches them in September is the other half of the deal: the extension bought time to file and none to pay, so the questions worth answering now are about money more than the calendar.

The 2025 deadlines, federal and Colorado

For individuals, Colorado lines up with the IRS. For partnerships and S corporations it doesn't, and that gap matters if you're waiting on a K-1.

Due in 2026 unless noted	IRS	Colorado
Individual return on extension (1040, DR 0104)	Oct. 15	Oct. 15
Tax owed on that return	Apr. 15	Apr. 15
Partnership or S corp return on extension (1065, 1120-S, DR 0106)	Sept. 15	Oct. 15
Last estimated payment for 2026, due in 2027	Jan. 15	Jan. 15

A deadline that lands on a weekend or legal holiday moves to the next business day, and none of these do. The federal partnership and S corporation deadline has already passed, which means a K-1 for your own return should be in hand. If it isn't, ask the business now, because your October 15 date doesn't move to wait for it. The small business return side of this has its own deadlines and penalties.

Is the deadline October 15 or October 17?

October 15. In 2026 it falls on a Thursday, so nothing shifts. The date only moves when the 15th is a weekend or holiday. In 2022 it was a Saturday and extended returns were due Monday, October 17, which is why that date still turns up in searches.

The other thing that moves a deadline is an IRS disaster postponement. We checked the IRS disaster relief list on September 18, and it shows no 2025 or 2026 postponements for any part of Colorado, so there's no extra time for Douglas County or anywhere else in the state.

Does a tax extension give you more time to pay?

No. It moved the filing date and nothing else. A federal extension comes from filing Form 4868, through IRS Free File or a preparer, or from making a payment in April and marking it as an extension payment. The IRS doesn't ask why, and any of those routes moves the filing deadline for a 2025 return from April 15 to October 15. The IRS says it plainly on its extension page: pay what you owe by the April date, because the extension is only for filing.

In practice the extension shields you from the failure-to-file penalty until October 15. Interest isn't touched at all, and the failure-to-pay penalty only goes away if you paid enough in April.

Does the IRS penalize you for filing an extension?

Not for the extension itself. What costs money is tax that wasn't paid by April 15, and a return that shows up after October 15.

The failure-to-pay penalty is 0.5 percent of the unpaid tax for each month or part of a month it stays unpaid, up to 25 percent. It has applied since April 15 to anyone who owed and didn't pay, extension or not, with one exception. If at least 90 percent of your total 2025 tax was paid by April 15 (through withholding, estimated payments, and whatever you sent with the extension) and you pay the rest when you file, the IRS treats you as having reasonable cause and waives this penalty for the extension period.

The failure-to-file penalty is ten times larger: 5 percent of the unpaid tax for each month or part of a month the return is late, capped at 25 percent. When both penalties hit in the same month, the filing penalty is reduced by the payment penalty, so the combined charge is 5 percent a month. A valid extension means this one hasn't started for you. It starts the day after October 15 if there's no return.

Interest sits apart from both penalties, and good behavior doesn't earn a waiver. The IRS charges it from April 15 until the tax is paid, compounded daily, at 6 percent a year for April through June and 7 percent from July onward. The IRS has already set 7 percent for October through December.

Suppose you owed $4,000 on April 15, paid nothing with the extension, and file and pay in full on October 15. That's six months of failure-to-pay penalty, $120, plus a little over $130 of interest. Annoying, but survivable. Now suppose the return goes in during mid-December instead, a bit more than 60 days late. Two months of the filing penalty would come to $360, but once a return is more than 60 days late the minimum is $525 or the full tax due, whichever is smaller, so the charge is $525. Missing October 15 by two months costs more than the whole six months before it.

How does Colorado's tax extension work?

Colorado gives every individual an automatic six-month extension to October 15. There's no form to file to claim it, and it doesn't depend on whether you extended your federal return. What Colorado doesn't extend is the payment: the Department of Revenue wants at least 90 percent of your 2025 Colorado tax paid by April 15. The DR 0158-I extension payment form is only for people who paid that amount by check or money order. If you paid through Revenue Online, you never needed it.

If you paid that 90 percent in April, file by October 15, and pay the remaining balance when you file, Colorado waives its late payment penalty and charges only interest on the balance. If you fall short on any of those, the penalty is the greater of $5 or 5 percent of the unpaid tax, plus 0.5 percent for each month it stays unpaid, capped at 12 percent. Colorado's 2026 interest rate is 11 percent, or 8 percent if you pay before the state issues a notice of deficiency. That's well above the IRS rate, which is a good reason not to leave the state balance for last.

Say your 2025 Colorado tax comes to $1,000. If you paid $900 in April and file with the last $100 by October 15, you owe a few dollars of interest and no penalty. If you paid $500 instead, you missed the 90 percent test, so the penalty starts at $25, which is 5 percent of the $500 shortfall, and adds half a percent a month from there, on top of interest.

How to pay what you owe before you file

Pay now, even if the return isn't finished. Interest runs daily on whatever is unpaid, so every payment made in September stops the meter on that amount. For federal tax, IRS Direct Pay takes a payment straight from a checking or savings account, and your IRS online account shows the payment afterward. Debit and credit card payments go through IRS-approved processors that charge a fee, and EFTPS works if you're already enrolled in it. For Colorado, Revenue Online is the simplest route. A check mailed with the Colorado return goes with the DR 0900 payment form.

Paying ahead doesn't change the 90 percent test, which looked only at April 15. It does keep the interest and the monthly payment penalty from growing on the amount you send.

What to gather in the next few weeks

Most returns go on extension because one document wasn't ready. Beyond that one missing piece, pull together:

Every 2025 tax payment with its date: withholding from your W-2s, any estimated payments, and the payment you made with the extension. Your IRS online account lists federal payments, and Revenue Online shows Colorado's.
Corrected forms, if a brokerage sent a revised 1099 after April.
Your 2024 return if we didn't prepare it.

Everything else is on our list of what to bring to a tax appointment. Getting it to a preparer by the end of September leaves time to chase down whatever turns out to be missing, and a return that shows up complete on October 13 is a very different job from one that shows up with a question mark.

Self-employed? October 15 is a retirement deadline too

If you extended, the deadline for a 2025 SEP-IRA contribution moved with your return. The IRS lets you deposit it any time up to the extended due date and still deduct it for 2025, even if you file before then. It's the one part of an extension that works in your favor, and it's easy to forget once the return is done. If your 2026 income is also coming in without withholding, our guide to quarterly estimated taxes covers the January 15 payment in the table above.

Can you get another extension after October 15?

For most people, no. The six months from Form 4868 is the only automatic extension, and there's no second form to file. The exceptions are narrow:

If you were living outside the U.S. on April 15, you had an automatic two months, Form 4868 extends that to October 15, and you can ask the IRS for a discretionary extension to December 15. The IRS has to approve it.
People serving in a combat zone get the time they serve there plus at least 180 days after they leave.
A return e-filed by October 15 and then rejected still counts as on time if it's corrected and resubmitted electronically by the fifth calendar day after, October 20. The fallback is a paper return mailed within ten calendar days of the rejection notice, with a note explaining why it's late.

What happens if you miss October 15?

The failure-to-file penalty begins on whatever federal tax is still unpaid, counted by the month, and a partial month counts as a full one. File as soon as you can, even a few days late, because each new month adds another charge. If your return shows a refund there's no penalty for filing late, but the IRS only pays refunds claimed within three years, so a refund left sitting long enough is simply lost.

On the Colorado side, missing October 15 removes the penalty waiver, so the late payment penalty applies to whatever wasn't paid by April 15, even if you met the 90 percent test. A Colorado refund is tracked separately from the federal one; where to check your Colorado refund covers how.

If the return shows more than you can pay

File by October 15 anyway. The filing penalty is the expensive one, and it's the only one you can still avoid completely. Then deal with the balance. The IRS offers a short-term plan of up to 180 days for balances under $100,000, and most individuals who owe $50,000 or less can set up a longer monthly plan online. Both require that all required returns be filed, which is one more reason the October return matters. We walk through the plan types, fees, and first-time penalty relief in can't pay your taxes? IRS payment plans explained.

Colorado runs its own payment plans, requested through Revenue Online or by calling the Department of Revenue at 303-205-8291. There's no setup fee, and standard plans for individuals run up to 36 months, but interest and penalties keep accruing while you pay, and any future Colorado refund goes to the balance.

What if you never filed an extension?

Then April 15 was your deadline, and the failure-to-file penalty has been building on any unpaid tax since then. Five months in, it has already reached its cap, while the failure-to-pay penalty and interest keep going. Filing now still helps. The interest and the payment penalty are figured on a balance you can start paying down, and your own return heads off a substitute return, which the IRS can prepare from the income records it has and which may not give you credit for the deductions you're entitled to.

People searching for how to file back taxes usually have more than one year open. The IRS generally looks for the last six years of returns before treating someone as current. Your IRS online account shows wage and income transcripts, meaning what employers, banks, and brokers reported, for up to the last ten years, which covers most of the income side. The current year and the two before it can be e-filed; older years are printed and mailed. A missing federal year is almost always a missing Colorado year too. Our page on back taxes and amended returns covers the rest.

When to bring in an enrolled agent

Plenty of people finish an extended return on their own. It's worth handing off when the return itself got complicated, say a K-1 or a home sale, or when you owe more than you can pay and want to know which plan fits before you commit to one. Unfiled years behind this one are another good reason to get help, because each of those years needs its own records rebuilt.

Charles Trautman is an IRS Enrolled Agent and has prepared individual, small business, and prior-year returns from the Lone Tree office since 2010. If you're weighing credentials, we explained the difference in enrolled agent vs. CPA. For an individual return on extension, documents can go up through our secure portal, so you don't have to come to Park Meadows to get this done.

Common questions

When is the tax extension deadline for 2025 returns?

Thursday, October 15, 2026, for both federal and Colorado individual returns. No IRS disaster postponement covers any part of Colorado, so there is no later date for anyone in the state.

Does a tax extension give me more time to pay?

No. Federal and Colorado tax for 2025 was due April 15, 2026. Interest has run on any unpaid balance since then, and a late payment penalty applies too unless you paid at least 90 percent by April 15 and pay the rest when you file.

Is there a penalty for filing a tax extension?

No. Filing Form 4868, or relying on Colorado's automatic extension, costs nothing. The penalties come from tax left unpaid after April 15 and from a return filed after October 15.

Do I need to file a form for a Colorado extension?

No. Colorado's six-month extension is automatic. The DR 0158-I form is only for sending an extension payment by check or money order, and a payment made through Revenue Online needs no form at all.

Can I get another extension after October 15?

Not in most cases. Americans living abroad can ask the IRS for a discretionary extension to December 15, and people serving in a combat zone get at least 180 days after they leave. A return e-filed by October 15 and rejected still counts as on time if it is corrected and resubmitted by October 20.

What happens if I miss the October 15 extension deadline?

The IRS failure-to-file penalty starts on any unpaid tax: 5 percent a month, up to 25 percent, with a minimum of $525 or the full tax due, whichever is smaller, once the return is more than 60 days late. Colorado's penalty waiver for extension filers also falls away. If you're owed a refund there's no penalty, but you have three years to claim it.

Can I still file if I never requested an extension?

Yes, and the sooner the better. The failure-to-file penalty has been building since April 15 on any unpaid tax. Filing is also a condition of an IRS payment plan, which requires every required return to be on file.

Sources

General information from Tax Shop in Lone Tree, Colorado, written by Charles Trautman, EA, and current as of September 18, 2026. IRS and Colorado interest rates change during the year, and every situation is different, so this isn't advice about your own return. Call and we'll look at where yours stands.