Introduction
October 15 is the final extended filing deadline for calendar-year C-corporations and for sole proprietors, freelancers, and single-member LLC owners who filed Form 4868 back in April. If that’s you, the return isn’t done yet, which means a few real tax-saving decisions are still on the table. Most of the “spend money to save money” advice you’ll find online no longer applies once the calendar has flipped past year-end, but a handful of genuinely valuable moves, including funding a retirement plan, claiming depreciation correctly, and optimizing your Qualified Business Income deduction, are still fully available right up until you file. This guide walks through exactly what’s still actionable, what’s already closed, and how to avoid the mistakes that turn a routine extension into an expensive one. Countsure works with small businesses and CPA firms through the extension crunch every year, so we’ve built this around the moves that actually move the needle.
Key Takeaways
- October 15 isn’t a universal deadline. It applies to extended individual returns (Form 1040, including Schedule C filers) and calendar-year C-corporations. S-corporations and partnerships had a September 15 extended deadline.
- SEP-IRA and Solo 401(k) employer contributions remain open. Sole proprietors, single-member LLCs, and C-corporations could fund these plans for the 2025 tax year right up to October 15 if they filed a valid extension.
- Traditional and Roth IRA contributions are already closed for 2025. Those deadlines were not extended and passed on April 15, 2026.
- Section 179 expensing rose sharply for 2025. The One Big Beautiful Bill Act (OBBBA) raised the limit to $2.5 million with a $4 million phase-out threshold.
- 100% bonus depreciation is back for 2025. Qualified property acquired and placed in service after January 19, 2025, qualifies for full first-year expenses.
- QBI deduction planning still matters at filing time. For 2025, the full 20% deduction is available below $197,300 (single) or $394,600 (married filing jointly), with a phase-in range above that.
- Missed depreciation from prior years can often be caught up without amending returns, using an accounting method to change on Form 3115.
- Filing an extension only postpones paperwork, not payment. Interest and failure-to-pay penalties continue accruing any 2025 balance still owed.
Who Actually Has Until October 15?
The short answer: individuals and C-corporations, not every business type. Extended deadlines depend entirely on how your business is taxed, and mixing these up is one of the most common, and costly, errors business owners make this time of year.
| Entity Type | Original 2025 Deadline | Extended Deadline | Extension Form |
| Sole proprietor / single-member LLC | April 15, 2026 | October 15, 2026 | Form 4868 |
| C-Corporation (calendar year) | April 15, 2026 | October 15, 2026 | Form 7004 |
| S-Corporation | March 16, 2026 | September 15, 2026 | Form 7004 |
| Partnership / multi-member LLC | March 16, 2026 | September 15, 2026 | Form 7004 |
| Trusts and estates | April 15, 2026 | September 30, 2026 | Form 7004 |
If you run an S-corp or partnership, your extended window is already closed in mid-September. What’s left for you now is damage control on late filing, not last-minute planning. Our guide on missing the S-corp deadline walks through the penalty relief options still available. For everyone else filing under an individual or C-corp extension, October 15 (a Thursday this year) is the real finish line, and it’s worth reviewing the full 2026 business tax deadlines calendar so nothing else slips past you in Q4.
Is There Still Time to Lower Your 2025 Tax Bill?
Partly. It helps to separate two different kinds of tax strategies. Spending-based deductions, such as buying equipment, prepaying expenses, and making charitable gifts, generally had to happen within the 2025 tax year for a cash-basis business, so those windows closed on December 31, 2025. What’s still open right now falls into a different category: elections, calculations, and a small number of contribution types that the IRS deliberately ties to your filing deadline rather than the calendar year.
That’s actually good news, because the moves that remain available tend to be the highest-value ones. A well-timed retirement contribution or a correctly claimed depreciation election can be worth more than most last-minute purchases would have been anyway.
If you’re unsure about which category a specific move falls into, that’s exactly the kind of question worth resolving before you file rather than after. Our team can review your 2025 numbers against the deadlines that still apply to your entity type and flag anything you might otherwise miss. Get in touch with our team before you submit your extended return. your extended return.
Fund a SEP-IRA or Solo 401(k) Before You File
This is the single largest lever most extension filers have left, and it’s frequently overlooked. Under IRS rules, a SEP-IRA can be opened and funded for the prior tax year as late as your business’s tax filing deadline, including extensions. The same logic applies to employer profit-sharing contributions in a Solo 401(k).
For sole proprietors, single-member LLCs, and C-corporations filing under an October 15 extension, that means you can still open a plan today and make a fully deductible 2025 contribution. For 2025, the SEP-IRA contribution limit is the lesser of 25% of compensation or $70,000. Solo 401(k) employer contributions follow the same combined limit, though employee elective deferrals for 2025 needed to have been elected before year-end.
A few distinctions matter here:
- SEP-IRA and Solo 401(k) employer contributions: deadline extends to your filing deadline, including extensions.
- Traditional and Roth IRA contributions: deadline was April 15, 2026, and was not extended by Form 4868. If you haven’t funded an IRA for 2025, that window is already closed.
- HSA contributions for 2025: also followed the April 15 deadline, not the extended one.
For a business owner with a strong 2025, a $40,000 to $70,000 SEP-IRA contribution funded in the next few weeks can meaningfully reduce taxable income on a return that hasn’t been filed yet, a rare opportunity to make a decision today that changes a return you’re about to submit.
Retirement plan timing decisions interact with your entity structure, cash flow, and overall filing strategy, so it’s worth reviewing before you commit funds. Our business tax services team can model out the deduction against your projected 2025 liability, so you know the number is worth funding before you wire it.
Claim Every Dollar of Section 179 and Bonus Depreciation You Qualify For
If your business bought equipment, machinery, software, or other qualifying property in 2025, the rules changed significantly mid-year, and many businesses haven’t updated their filing approach to reflect it. The One Big Beautiful Bill Act (OBBBA), signed in July 2025, made two major changes that apply directly to the return you’re about to file.
Section 179 expensing jumped to a maximum deduction of $2,500,000 for tax years beginning in 2025, with the phase-out threshold rising to $4,000,000 of qualifying purchases. That’s roughly double the pre-OBBBA limits, which means businesses that assumed they’d exceeded the old cap may not have exceeded the new one.
Bonus depreciation returned to 100% for qualified property acquired and placed in service after January 19, 2025. Property acquired before that date generally remains subject to the lower 40% rate that was in effect before the law changed, so the acquisition date matters as much as the purchase itself.
These aren’t automatic; they’re elections made on Form 4562 when the return is filed, which is exactly why it’s worth confirming your fixed asset records are accurate before your preparer finalizes anything. Our breakdown of the OBBBA’s new deductions covers how the law affects different entity types in more detail.
Don’t Leave the QBI (Section 199A) Deduction on the Table
The Qualified Business Income deduction lets eligible pass-through owners, including sole proprietors, partners, and S-corp shareholders, deduct up to 20% of qualified business income. For 2025, the OBBBA made this deduction permanent, removing the sunset date that had created planning uncertainty for years.
| Filing Status | Full Deduction Below | Phase-In Range | Wage/Property Limits Apply Above |
| Single / Head of Household | $197,300 | $197,300 to $247,300 | $247,300 |
| Married Filing Jointly | $394,600 | $394,600 to $494,600 | $494,600 |
Below the lower threshold, most owners get the full 20% deduction with no wage limitations. Inside the phase-in range, the deduction can be reduced based on W-2 wages paid and the qualified property your business holds, which is why the salary-versus-distribution balance for S-corp owners deserves a second look before filing, not after. A reasonable compensation figure that’s too high can shrink the QBI deduction unnecessarily; one that’s too low creates its own compliance risk.
If your 2025 taxable income lands anywhere near these thresholds, small, legitimate adjustments to retirement contributions or timing can shift you into a more favorable band. This is precisely the kind of calculation that benefits a second set of eyes before the return goes out. Our team can review your QBI calculation against the final numbers to confirm you’re claiming the full amount you’re entitled to.
Catch Up Missed Depreciation Without Amending Old Returns
Here’s a strategy most small business owners don’t know exists: if you’ve been under-depreciating an asset for one or more prior years, a common issue when books are kept in-house without close attention to fixed asset schedules, you generally don’t need to amend those old returns to fix it. Instead, an accounting method change filed on Form 3115 can let you catch up on the missed depreciation as a single adjustment on the current year’s return.
This matters for extension filers specifically because it’s a paperwork fix, not a spending decision, which means it’s still fully available even though 2025 has ended. If your fixed asset register hasn’t been reconciled against your depreciation schedules in a while, this is worth checking before you file rather than discovering the gap next year.
Consider the R&D Expense Pull-Forward Opportunity
Businesses that incurred domestic research and development costs between 2022 and 2024 have a specific opportunity tied to the OBBBA that’s easy to miss during a routine extension filing. The law restored the ability to fully deduct domestic R&D expenditures rather than amortizing them over five years, and it allows all taxpayers with eligible unamortized domestic R&D amounts from prior years to pull those amounts forward into the 2025 tax year, subject to the applicable rules. For a business that capitalized software development, product engineering, or process-improvement costs under the older rules, this can represent a meaningful one-time reduction to 2025 taxable income, though it requires coordination with how those costs were originally reported, so it’s not something to attempt without reviewing the underlying filings first.
Don’t Forget the September 15 Estimated Payment While You Focus on October 15
It’s easy to get tunnel vision on the extended filing deadline and lose track of ongoing obligations running in parallel. If your business makes quarterly estimated tax payments, the third-quarter 2026 installment was due September 15, before the October 15 filing deadline, not after it. Missing it doesn’t affect your extension, but it does trigger underpayment of penalties that accrue independently of your filing status.
Filing an extension only postpones the paperwork; it never postpones payment. If you estimated your 2025 balance conservatively back in April and it turns out you owe more once the return is finalized, interest has been accruing that gap since April 15 regardless of the extension. Confirming your 2025 balance and your 2026 estimated payments in the same review avoids surprises on both fronts. Our late filing penalty guide breaks down exactly how these penalties stack if a payment or a filing slip.
Common Last-Minute Mistakes That Cost Small Businesses Money
Rushing a return in the final weeks before October 15 tends to produce the same handful of errors every year:
- Confusing the extended deadline with the payment deadline. The extension moves the filing date, not the payment date; any 2025 balance still owed has been accruing interest since April 15.
- Missing state-level deadlines and elections. A federal extension doesn’t automatically extend state filing requirements, and some states require separate Pass-Through Entity Tax (PTET) elections on their own schedule.
- Filing without reconciling books first. A rushed return built on incomplete bookkeeping is more likely to contain errors, and inconsistent numbers are a known trigger for closer IRS scrutiny. Our guide to common IRS audit triggers covers the patterns worth avoiding.
- Skipping the accountable plan review. Reimbursements that don’t follow an accountable plan can become taxable wages, adding unexpected payroll tax exposure late in the process.
- Overlooking the retirement contribution window entirely. Many owners assume all contribution deadlines passed in April, missing the SEP-IRA and Solo 401(k) opportunity described above.
Getting Your 2025 Return Right Before October 15
The moves that are still available to you this close to the deadline aren’t about spending more money; they’re about making sure every dollar you already earned, saved, and invested in 2025 is reflected correctly on paper. Funding a SEP-IRA, confirming your Section 179 and bonus depreciation elections, and getting the QBI calculation right can add up to a materially different tax bill than a return filed on autopilot. Countsure works with small business owners and CPA firms every extension season to review these numbers before they’re locked in, not after. If your October 15 filing is still open, reach out to our team and we’ll help you confirm you’re not leaving anything on the table.
Frequently Asked Questions
1. Does the October 15 deadline apply to my LLC?
It depends on how your LLC is taxed. Single-member LLCs taxed as sole proprietorships follow the individual extended deadline of October 15. Multi-member LLCs taxed as partnerships, or LLCs that elected S-corp status, had an extended deadline of September 15.
2. What happens if I miss the October 15 deadline?
You’ll face a failure-to-file penalty of 5% of unpaid tax per month, up to 25% total, plus a separate failure-to-pay penalty and accruing interest. Filing as soon as possible after a missed deadline stops additional penalties from compounding further.
3. Can I still make retirement contributions after October 15?
For SEP-IRAs and Solo 401(k) employer contributions tied to the 2025 tax year, October 15 is the final date if you’re filing under an individual or C-corp extension. Traditional and Roth IRA contributions for 2025 were not extended and closed on April 15, 2026.
4. Is October 15 the deadline for S-corps too?
No. S-corporations and partnerships that filed Form 7004 had an extended deadline of September 15, 2026. October 15 applies to individual returns (including Schedule C filers) and calendar-year C-corporations.
5. Do I need to pay anything by October 15, or just file?
You should have already paid your estimated 2025 tax liability by April 15, 2026, when you filed the extension. October 15 is a filing deadline, not a payment deadline; any unpaid balance has been accruing interest since April regardless of the extension.
6. Can I still claim Section 179 for equipment I bought earlier in 2025?
Yes. Section 179 and bonus depreciation elections are made when you file your return, not when you purchase the asset, so equipment placed in service anytime during 2025 can still be claimed on a return filed by October 15.
7. What if I haven’t made my third quarter estimated payment yet?
The September 15, 2026 deadline for Q3 estimated payments has already passed. Paying it as soon as possible limits further underpayment penalties, even though it’s technically late.
8. Should I file even if I can’t pay the full amount I owe?
Yes. Filing on time (or by your extended deadline) avoids the larger failure-to-file penalty even if you can’t pay in full. The failure-to-pay penalty on the remaining balance is smaller than the failure-to-file penalty, so filing first and arranging payment separately is almost always the better outcome.
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Parth Shah, Managing Director
(CPA-US, FCA, RV-S&FA, DISA)
Parth Shah who is head of Accounts and Book keeping has experience of more than 10 years. A Certified Public Accountant – US, fellow Chartered Accountant, Registered Valuer and Diploma in Information System Audit.
