The October 15 Deadline for Practice Owners: What Is Still Possible

October 15 is the extended due date for individual returns — the end of the six-month extension filed back in April. Like September 15 for the practice return, it is terminal. There is no further extension for a personal return.

It is also the last date on which a small number of prior-year tax moves remain available. Understanding which ones is the difference between a productive October and an expensive assumption.

What the April Extension Did and Did Not Do

Form 4868 extended the deadline to file. It never extended the deadline to pay.

Tax owed for the prior year was due April 15 regardless of the extension. Any balance unpaid since then has been accruing:

• Failure-to-pay penalty at 0.5% per month, capped at 25%
• Interest at the federal short-term rate plus three percentage points, adjusted quarterly

This is the most expensive misunderstanding on the calendar. An owner who extended in April believing the balance was also deferred has been running a penalty and interest meter for six months without knowing it.

If a balance is owed, paying as much as possible now — before filing, if the return is not ready — reduces what continues to accrue.

What Can Still Be Done for the Prior Year

Short list. That is the honest answer, and it is worth stating plainly because October generates a lot of hopeful questions.

Retirement contributions tied to an extended return. This is the main live lever. Employer contributions such as a SEP-IRA generally follow the due date of the return on which they are deducted, including extensions.

Choosing among available elections and methods on a return not yet filed. Some elections are made with the return rather than during the year, so they remain open until the return is filed. Which ones apply is fact-specific and worth asking about directly.

Accurate substantiation. Not glamorous, but October is the last chance to properly document deductions the practice actually earned — mileage logs, home office measurements, continuing education records. Documentation assembled now supports a deduction; documentation assembled after a notice arrives is worth considerably less.

What Closed on December 31

Most tax planning requires something to have happened during the tax year, not to be recorded afterward. These are gone:

• Equipment and technology purchases. Section 179 and bonus depreciation require the asset to be placed in service during the year. A dental chair or imaging system bought in October of the following year is a current-year deduction, not a prior-year one.
• Charitable contributions. Deductible in the year given.
• Owner salary adjustments. Reasonable compensation runs through payroll, and payroll for a closed year is closed. This is why September and October matter for the current year — there is still payroll runway now that will not exist in December.
• Entity elections and structure changes. Generally prospective or bound by their own separate deadlines.
• Timing of income and expenses. For a cash-basis practice, when a payment was actually received or made is a fact, not an election.

The pattern is consistent: the levers that move real money required a decision inside the year. October is for filing accurately, not for finding savings that were never created.

Free tool: Year-End Tax Playbook — the moves that are still open for the current year, emailed in 90 seconds.

The Retirement Contribution Deadline Owners Get Wrong

This one deserves its own section because the error is specific, common, and costs real money.

The rule: employer retirement contributions generally follow the due date of the return they are deducted on, including extensions.

For a practice owner, that means the answer depends on entity structure:

• SEP-IRA deducted on an extended personal return (a sole proprietor, or a single-member LLC without an S-corp election) — October 15.
• SEP-IRA for an S-corp practice, where the contribution is a practice-level deduction on the extended 1120-S — September 15.
• Traditional and Roth IRA contributions — April 15, and extensions do not move this one at all.
• Establishing a new solo 401(k) — rules changed under SECURE 2.0 and depend on entity type and whether employee deferrals are involved. Genuinely fact-specific; confirm before relying on it.

The failure mode is an owner who has heard “you have until October 15 to fund your SEP,” operates through an S-corp, and discovers the contribution actually rode on the practice return a month earlier. The general advice is correct for sole proprietors and wrong for S-corp owners, and most practice owners with meaningful income are S-corp owners.

Go deeper: Retirement Account Options for a Physician Practice · Free tool: Retirement Optimizer

What If the K-1 Has Not Arrived?

An owner cannot accurately complete a personal return without the Schedule K-1 reporting their share of practice income. When the practice return was late, this is where it lands.

The general principle mirrors September: failure-to-file is the more expensive penalty, at 5% of unpaid tax per month against 0.5% for failure-to-pay. Filing on the best available figures and amending later usually beats missing October 15.

The costs of that path are real, though — interest on any shortfall, and an amended return for each affected owner. And it is a decision to make with your CPA on the specific numbers, not a default.

The structural fix is upstream and worth naming: the practice return is due September 15 precisely so that owners have four weeks. When that buffer exists, this problem does not.

Go deeper: What Happens If Your Practice Misses September 15

What October Should Actually Be Used For

If the personal return is handled, October is the highest-leverage planning month left in the year — not for the year being filed, but for the year still running.

Roughly ten weeks remain. Enough time for:

• Owner salary correction. Reasonable compensation can still be adjusted across remaining payroll runs. In December it cannot.
• Q4 estimated payment sizing. Due January 15, and the last opportunity to true up.
• Equipment decisions. Assets placed in service by December 31 count for the current year.
• Retirement plan setup for the current year, where establishment deadlines still allow it.

The practices that are never scrambling in October are running that planning conversation in October — about the year in front of them, while there is still time to act on the answer.

Related: Tax Deadlines for Practice Owners: The Full Calendar · Reasonable Compensation for a Physician S-Corp · Quarterly Estimated Taxes for a Physician Practice

This article describes general federal rules for calendar-year filers and is not tax advice for a specific situation. Penalty amounts noted as indexed adjust annually. Retirement plan deadlines depend on entity type and plan documents — confirm yours before relying on a general rule.