Tax Deadlines for Physician and Dental Practice Owners: The Full Calendar

Four dates run a practice owner’s tax year: March 15 and September 15 for the practice return, April 15 and October 15 for the personal return. Everything else — estimated payments, payroll filings, information returns — hangs off that frame. Miss one of the four and the cost is rarely the tax; it is the penalty structure attached to the date.

This is the full calendar for a calendar-year physician, dental, or med spa practice, with what each deadline actually covers and what missing it costs.

What Are the Practice Return Deadlines?

March 15 — Calendar-year S-corporation returns (Form 1120-S) and partnership returns (Form 1065) are due. This is a month earlier than the personal deadline by design: the practice return produces the Schedule K-1s that owners need to file personally.

September 15 — The extended due date, if Form 7004 was filed in March. The extension is six months, and it is the only one available. There is no second extension and no grace period.

The ordering is the part practice owners most often miss. The practice return is not simply one of several filings — it is the input to every owner’s personal return. A late 1120-S does not just incur its own penalty; it strands each owner’s 1040 four weeks before their own extended deadline.

Go deeper: What Is the September 15 Deadline for a Physician Practice?

What Are the Personal Return Deadlines?

April 15 — Form 1040 is due. Filing Form 4868 extends the filing deadline to October 15 but does not extend the deadline to pay. Tax owed on April 15 that is paid in October accrues interest and, in most cases, a failure-to-pay penalty running at 0.5% per month up to a 25% maximum.

October 15 — The extended personal deadline. Like September 15 for the practice, this one is terminal.

The extension-is-not-a-payment-extension point is worth stating plainly because it is the single most expensive misunderstanding in the calendar. An owner who extends in April believing the balance is also deferred is accruing penalty and interest for six months without knowing it.

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

When Are Estimated Tax Payments Due?

For calendar-year individuals: April 15, June 15, September 15, and January 15 of the following year.

Two structural facts cause most of the trouble:

The quarters are not quarters. The first payment covers January through March, the second covers April and May — two months — the third covers June through August, and the fourth covers September through December. An owner dividing an annual estimate into four equal payments is systematically underpaid in the first half of the year.

September 15 collides with the practice return. The Q3 payment and the extended practice return share a date. Handling one does not handle the other.

Safe-harbor rules generally protect an owner from underpayment penalties who pays either 100% of the prior year’s total tax (110% if prior-year adjusted gross income exceeded $150,000) or 90% of the current year’s tax. For a practice whose income is climbing, the prior-year safe harbor is usually the cheaper and more certain path — it is a known number in advance rather than an estimate of a year still in progress.

Go deeper: Quarterly Estimated Taxes for a Physician Practice · Free tool: Estimated Tax Calculator

What Payroll and Information-Return Deadlines Apply?

January 31 — W-2s to employees and to the Social Security Administration; 1099-NEC to contractors and to the IRS. A practice with locum tenens coverage, contracted hygienists, or an outside billing company usually has more 1099 obligations than the owner expects, and the penalty is per form.

Quarterly (April 30, July 31, October 31, January 31) — Form 941 payroll tax returns.

Each payroll run — Federal tax deposits, on either a monthly or semiweekly schedule depending on the practice’s deposit history. Deposit penalties escalate with lateness: they start at 2% and reach 15% once the deposit is more than 10 days past a notice.

For an S-corp practice, payroll is not administrative housekeeping. The owner’s reasonable compensation is set through it, and the salary figure is what makes the S-corp election defensible.

Go deeper: Reasonable Compensation for a Physician S-Corp · Free tool: S-Corp Salary Optimizer

What Does Missing Each Deadline Actually Cost?

The penalties are not uniform, and the differences drive which deadlines deserve the most attention.

Practice return (1120-S / 1065) filed late — Roughly $250 per owner, per month or part of a month, indexed annually for inflation, for up to 12 months. It applies even when the practice owes no tax. This is the most disproportionate penalty on the calendar: a paperwork failure on a zero-tax return, multiplied by the number of owners.

Personal return filed late — 5% of unpaid tax per month, capped at 25%. If the return is more than 60 days late, a minimum penalty applies equal to the lesser of a set dollar amount (indexed annually) or 100% of the tax owed.

Tax paid late — 0.5% per month, capped at 25%, plus interest at the federal short-term rate plus three percentage points, adjusted quarterly.

Estimated payments missed or short — Underpayment interest charged per quarter. There is no flat penalty; the cost is a function of how much was short and for how long.

Note the asymmetry: filing late is far more expensive than paying late. An owner who cannot pay should still file. The 5% monthly failure-to-file penalty is ten times the 0.5% failure-to-pay penalty, so filing on time and arranging payment afterward is almost always the cheaper sequence.

Go deeper: What Happens If Your Practice Misses the September 15 Deadline?

What Deadlines Apply to Retirement Contributions?

Employer retirement contributions generally follow the due date of the return they are deducted on, including extensions:

• SEP-IRA for an S-corp practice — Tied to the practice return, so September 15 if extended.
• SEP-IRA deducted on an extended personal return — October 15.
• Traditional and Roth IRA contributions — April 15, and extensions do not move this one.
• Establishing a new solo 401(k) — Rules here changed under SECURE 2.0 and depend on entity type and whether employee deferrals are involved; the timing is genuinely fact-specific and worth confirming before relying on it.

The S-corp versus personal distinction on the SEP is the one that causes real losses. An owner who has heard “you have until October 15 to fund it” and whose contribution actually rides on the practice return has a month less than they think.

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

What Should a Practice Owner Do With This Calendar?

Work backward from the two hard stops.

For September 15: the practice books need to be closed by roughly mid-August for the return to be prepared without a scramble. If the books are not closed by the first week of September, that is the signal to act — not September 14.

For October 15: the owner’s K-1 must exist first. A practice return filed on September 15 leaves four weeks, which is workable. A practice return filed late compresses that to nothing.

The practices that never have a deadline problem are not the ones with better calendars. They are the ones whose monthly close finishes early enough that the return is a formality rather than a reconstruction project.

Related: The Complete Tax Guide for Physician Practices · Free tool: Year-End Tax Playbook

This article describes general federal rules for calendar-year practices and is not tax advice for a specific situation. State deadlines, fiscal-year entities, and practices with multiple entities or multi-state activity carry additional dates not covered here. Penalty amounts noted as indexed adjust annually.