Does filing a late return trigger an audit?

Filing on extension is not a red flag for audits. It's common and legitimate — the IRS issues automatic extensions without review. An extended return filed by the extended due date is not 'late' in the IRS system. A return filed after the extended deadline without an extension is late, which does increase scrutiny slightly.

What if I file an extension but can't pay anything by April 15?

The extension protects you from the failure-to-file penalty (5% per month, up to 25%) but not the failure-to-pay penalty (0.5% per month, up to 25%). You should pay as much as you can by April 15 to minimize penalty and interest accrual. If you genuinely can't pay, contact the IRS about a payment plan (installment agreement) — the IRS typically grants these and the penalties are more manageable than ignoring the liability.

My S-corp extended its return to September 15. Do I also need to extend my personal return?

Almost always yes — your personal return requires the Schedule K-1 from the S-corp, which won't be ready until after the corporate extension deadline. File Form 4868 for yourself by April 15 to extend your personal return to October 15. This gives 30 days after the September 15 S-corp deadline to prepare your personal return with the final K-1.

Can I extend my IRA or HSA contribution deadline by filing an extension?

Yes — filing an extension for your personal return gives you until the extended due date (October 15) to make SEP-IRA contributions. HSA contributions can also be made until October 15 with an extension. Solo 401(k) contributions are different: employee deferrals must be made by December 31 of the plan year, but employer (profit-sharing) contributions can be made by the return due date including extensions.

Are there penalties for not filing the return even if I've paid all the taxes?

Technically yes — failure to file carries a minimum penalty of the lesser of $510 or 100% of the tax due. But if you owe zero taxes, the failure-to-file penalty is $0 (since it's a percentage of tax owed). However, there are other reasons to file even if you owe nothing: to start the statute of limitations clock on potential IRS examination and to claim any refund (which has a 3-year claim deadline).

Tax planning

Tax Extensions Explained: What Filing an Extension Does (and Doesn't) Do

Filing a tax extension gives you more time to file your return — not more time to pay. If you owe taxes, interest and late payment penalties accrue from the original deadline even with an extension filed. Here's what extensions cover, what they don't, and when they make sense.

Written by Matt Reese, CPA · 5 min read · Published April 2026·Share on LinkedIn

Key Takeaways

A tax extension gives you an automatic 6-month extension to file your return — not to pay your taxes. Any taxes owed are still due on the original deadline (typically April 15 for individuals and S-corps on a calendar year).
If you file an extension but owe taxes and don't pay by the original deadline, you'll owe late payment penalties (0.5% per month) plus interest (currently around 8% annually), even though the extension was filed.
Extensions are automatic — you don't need to explain why or provide documentation. File Form 4868 (individual) or Form 7004 (business returns) by the original due date.
The most legitimate reason to extend: waiting for K-1s. Partnerships and S-corps have until March 15 to file (or September 15 on extension), which means your K-1 may not arrive until September. Extending your personal return to October 15 is then required.

The critical distinction: extension to file vs extension to pay

This is the most common misunderstanding about tax extensions: an extension gives you more time to file your return, not more time to pay taxes.

Your tax liability is calculated as of December 31. It becomes due on the original filing deadline regardless of whether you extend. If you owe $20,000 and file an extension without paying, you owe $20,000 plus:

Late payment penalty: 0.5% per month (or fraction) of the unpaid tax, up to 25%
Interest: Federal short-term rate + 3%, currently around 7–8% per year, compounded daily

The extension eliminates the failure-to-file penalty(5% per month, up to 25%) — which is the more expensive of the two penalties. If you know you owe taxes but can’t finish the return by April 15, always file an extension. Even with the late payment penalty running, you avoid the much larger failure-to-file penalty.

File the extension even if you can’t pay a dollar. The failure-to-file penalty (5%/month) is ten times larger than the failure-to-pay penalty (0.5%/month). Eliminating the larger one is always worth it.

Key filing deadlines and extended deadlines

Return type	Form to extend	Original deadline	Extended deadline
Individual (Form 1040)	Form 4868	April 15	October 15
S-corporation (Form 1120-S)	Form 7004	March 15	September 15
Partnership (Form 1065)	Form 7004	March 15	September 15
C-corporation (Form 1120, calendar year)	Form 7004	April 15	October 15
Estate or trust (Form 1041)	Form 7004	April 15	September 30
FBAR (FinCEN 114, foreign accounts)	Automatic	April 15	October 15

March 15 catches S-corp owners off guard

Individual returns are due April 15, but S-corp returns (Form 1120-S) are due March 15 — a month earlier. If you have an S-corp, your accountant needs to file the corporate return (or extension) by March 15, and the K-1 that flows to your personal return comes from that filing. If the corporate return is extended, so is your K-1 — which is why personal returns with S-corp K-1s are almost always extended.

How to file an extension

Extensions are filed with the IRS by the original due date:

Form 4868 (individual): File electronically through your tax software, IRS Free File, or your CPA. Takes 5 minutes. No reason or documentation required.
Form 7004 (business entities): Filed for S-corps, partnerships, trusts, and C-corps. Same process — file by the entity’s original deadline.
Payment with the extension: If you expect to owe taxes, include a payment with the extension. The IRS accepts electronic payment through EFTPS or IRS Direct Pay. Your CPA will estimate what you owe.

The extension is automatic— the IRS doesn’t review or approve it. File the form by the deadline and the extension is granted.

Legitimate reasons to extend

Situation	Why extension makes sense
Waiting for K-1s from partnerships or S-corps	K-1s may not arrive until September. Extension required to include them accurately.
Complex year with business sale, RSUs, or major transactions	More time to get the analysis right reduces errors and reduces audit risk.
Tax documents arriving late (1099s, corrected forms)	Brokerage and fund 1099s are often corrected in March — extending avoids amended returns.
CPA capacity constraints in busy season	CPA quality at 11 PM on April 14 is lower than quality in May. Extension enables better work.
Business just started and financials aren't finalized	Books need to be closed and reviewed before the return can be prepared accurately.

Penalty comparison — $25,000 owed, filed October 14 (on extension)

Taxes owed$25,000

Payment made with extension on April 15 (estimates)$20,000

Remaining balance unpaid after April 15$5,000

Failure-to-pay penalty: 0.5% × $5,000 × 6 months$150

Interest on $5,000 balance at 8%/year for 6 months≈ $200

Total additional cost≈ $350

Failure-to-file penalty if extension NOT filed: 5% × $25,000 × 6 months$7,500 (capped at 25% = $6,250)

Paying $20,000 on April 15 and extending to October for the balance costs about $350 in extra fees. Not filing an extension on the same facts would cost over $6,000 in failure-to-file penalties alone — 17x more. Always file the extension.

Your CPA files the extension — you don't need to think about it

If you work with a CPA, they handle all extensions as a matter of course. The thing to ensure: pay your CPA enough information by early April to estimate what you owe so they can include a payment with the extension. Flying blind on the extension amount and underpaying is what creates the late payment penalties.

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Frequently asked

Questions owners actually ask

Does filing a late return trigger an audit?: Filing on extension is not a red flag for audits. It's common and legitimate — the IRS issues automatic extensions without review. An extended return filed by the extended due date is not 'late' in the IRS system. A return filed after the extended deadline without an extension is late, which does increase scrutiny slightly.
What if I file an extension but can't pay anything by April 15?: The extension protects you from the failure-to-file penalty (5% per month, up to 25%) but not the failure-to-pay penalty (0.5% per month, up to 25%). You should pay as much as you can by April 15 to minimize penalty and interest accrual. If you genuinely can't pay, contact the IRS about a payment plan (installment agreement) — the IRS typically grants these and the penalties are more manageable than ignoring the liability.
My S-corp extended its return to September 15. Do I also need to extend my personal return?: Almost always yes — your personal return requires the Schedule K-1 from the S-corp, which won't be ready until after the corporate extension deadline. File Form 4868 for yourself by April 15 to extend your personal return to October 15. This gives 30 days after the September 15 S-corp deadline to prepare your personal return with the final K-1.
Can I extend my IRA or HSA contribution deadline by filing an extension?: Yes — filing an extension for your personal return gives you until the extended due date (October 15) to make SEP-IRA contributions. HSA contributions can also be made until October 15 with an extension. Solo 401(k) contributions are different: employee deferrals must be made by December 31 of the plan year, but employer (profit-sharing) contributions can be made by the return due date including extensions.
Are there penalties for not filing the return even if I've paid all the taxes?: Technically yes — failure to file carries a minimum penalty of the lesser of $510 or 100% of the tax due. But if you owe zero taxes, the failure-to-file penalty is $0 (since it's a percentage of tax owed). However, there are other reasons to file even if you owe nothing: to start the statute of limitations clock on potential IRS examination and to claim any refund (which has a 3-year claim deadline).

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Educational content only.This article is for informational purposes and does not constitute tax, legal, or investment advice. Every owner’s facts are different; consult a qualified CPA and advisor before acting. Tax and accounting services are provided through Matt Reese, CPA; investment advisory services are provided through Measured Risk Portfolios, a registered investment adviser. Matt Reese, CPA and Measured Risk Portfolios are separate entities; clients are not required to engage both.