When Are Small Business Taxes Due?

For the 2025 tax year, most small business income-tax returns are due in the first half of 2026: S-corporations (Form 1120-S) and partnerships (Form 1065) file by March 16, 2026, while sole proprietors (Schedule C), single-member LLCs, and C-corporations (Form 1120) file by April 15, 2026. But the annual return is only one deadline. If your business owes $1,000 or more in tax, you also owe quarterly estimated payments throughout the year (April 15, June 15, September 15, and January 15), and if you have employees, payroll tax deposits run on a separate monthly or semi-weekly schedule. This guide lays out every date, explains the March-versus-April split, and shows how to keep the cash on hand when those bills land.

The core 2026 filing deadlines by entity type

The single most common mistake owners make is assuming every business files in April. It doesn't work that way — pass-through entities file about a month earlier so their owners can receive a K-1 in time for their own personal returns. Here is the 2025-tax-year calendar (returns filed in 2026):

• Partnerships (Form 1065) — due March 16, 2026 (the 15th falls on a Sunday). Extension to September 15, 2026.
• S-corporations (Form 1120-S) — due March 16, 2026. Extension to September 15, 2026.
• Sole proprietors & single-member LLCs (Schedule C with Form 1040) — due April 15, 2026. Extension to October 15, 2026.
• C-corporations (Form 1120) — due April 15, 2026 for calendar-year filers. Extension to October 15, 2026.

Two things to internalize. First, an extension gives you more time to file, never more time to pay — any tax owed is still due on the original deadline, and interest and penalties accrue from that date. Second, fiscal-year businesses (those that don't close their books on December 31) follow a shifted schedule: the return is generally due the 15th day of the third or fourth month after year-end, depending on entity type.

Quarterly estimated taxes: the deadlines that catch people off guard

The federal income-tax system is pay-as-you-go. If you expect to owe $1,000 or more when you file (or $500+ for a C-corp), the IRS wants the money in installments across the year — not in one April lump. This applies to most self-employed owners, partners, and S-corp shareholders, because no employer is withholding tax from that income.

For the 2026 tax year, federal estimated payments are due:

• Q1 (Jan 1 – Mar 31 income): April 15, 2026
• Q2 (Apr 1 – May 31 income): June 15, 2026
• Q3 (Jun 1 – Aug 31 income): September 15, 2026
• Q4 (Sep 1 – Dec 31 income): January 15, 2027

Note the quarters are not even three-month blocks — Q2 covers only two months and Q4 covers four. Miss a payment or underpay, and the IRS charges an underpayment penalty calculated as interest on the shortfall, even if you pay in full by April. Many owners use the safe harbor: pay at least 100% of last year's tax liability (110% if your prior-year adjusted gross income topped $150,000) and you avoid the penalty regardless of how the current year turns out.

Payroll and self-employment taxes run on their own clock

If you have W-2 employees, payroll taxes are the deadlines that never sleep. You're depositing withheld income tax plus both halves of Social Security and Medicare on either a monthly or semi-weekly schedule, which the IRS assigns based on your lookback-period liability. On top of the deposits, you file Form 941 quarterly (end of April, July, October, and January) and Form 940 (federal unemployment) annually by January 31. W-2s and 1099-NECs must be furnished to recipients and filed by January 31 as well.

Self-employed owners without employees don't run payroll, but they do pay self-employment tax — the full 15.3% for Social Security and Medicare — through those quarterly estimates above. Payroll deposit penalties escalate fast (from 2% up to 15% depending on how late), so if cash is ever going to be tight, the payroll deposit is the last bill you want to skip. It is money you're holding in trust for employees and the government, and the IRS pursues it aggressively.

A realistic deadline calendar (example)

Here's how the year actually looks for a typical S-corp with a couple of employees. Figures are illustrative — for example only — to show the rhythm of the obligations, not a prediction of your bill.

The pattern to see: three or four meaningful cash outflows cluster in spring and early fall. If your revenue is seasonal, some of those dates may land in your slowest months — which is exactly the planning problem the next two sections address.

Decision framework: what to do when a deadline lands and the cash isn't there

Underwriters see this constantly — a profitable business with a real tax bill and a temporary cash gap because receivables haven't landed yet. Work the problem in this order:

1. File on time no matter what. The failure-to-file penalty (5% per month) is roughly ten times the failure-to-pay penalty (0.5% per month). Even if you can't pay a dollar, file or extend by the deadline to kill the larger penalty.
2. Pay what you can toward the balance. Penalties and interest accrue only on the unpaid portion, so a partial payment directly shrinks the meter.
3. Consider an IRS payment plan. Businesses that owe under $25,000 can often set up an installment agreement online. Interest still runs, but it stops the account from escalating to liens or levies.
4. Protect payroll deposits first. If you must choose what to short, never short trust-fund payroll taxes — the penalties and personal liability there are the harshest in the code.
5. Bridge a short gap with revenue-based financing when the timing — not the solvency — is the problem. If you have the sales but the deposit dates simply don't line up with the tax dates, a revenue-based advance can cover the deadline and repay as your deposits come in. It's a timing tool, not a substitute for a business that can't cover the bill.

The honest test: is this a timing problem or a profitability problem? Financing solves the first and buries the second. See our business funding guide for how to tell them apart before you borrow.

Using revenue-based financing to smooth tax-deadline cash flow

When a quarterly estimate or a payroll deposit lands during a slow stretch, some owners bridge it with a revenue-based advance or MCA-style marketplace rather than draining operating cash. The reason it fits tax timing specifically: approval leans on your bank deposits and monthly revenue rather than your credit score, so a strong-selling business with a thin or bruised personal file can still qualify. Typical marketplace parameters look like: funding from about $10,000 and up, FICO 500+ considered, decisions in 24–48 hours, and repayment that flexes as a small slice of daily or weekly deposits — so the payback tracks your cash flow instead of demanding a fixed sum on a dead-slow week.

Match the tool to the situation. This works when you have the sales to comfortably service the advance and the tax bill is a scheduling mismatch. It's the wrong tool if the tax debt reflects a structural loss — in that case, an IRS installment agreement and a conversation with your accountant beat any financing. No legitimate funder should ever describe approval as "guaranteed," and any that does is a red flag. Used deliberately for a genuine timing gap, though, a revenue-based bridge keeps you filing and paying on time without starving payroll or inventory. Our funding pillar walks through how to size an advance against your deposit volume.

Extensions, penalties, and the mistakes that cost the most

A few clarifications that save owners real money every year:

• An extension is not a payment plan. Filing Form 7004 (business) or 4868 (personal) buys you six months to submit paperwork, but 100% of the tax is still due on the original date. Estimate and pay with the extension.
• Estimated-tax underpayment is a penalty even in a great year. If you had a breakout year and didn't raise your quarterly payments, you can owe a penalty in April despite paying the full balance. Recalculate estimates mid-year when revenue jumps.
• State deadlines don't always match federal. Most states track the federal dates, but franchise taxes, gross-receipts taxes, and sales-tax filings run on their own state calendars. Check your specific state.
• Disaster-area postponements happen. When the IRS declares a disaster relief zone, filing and payment deadlines in affected counties are pushed back automatically — worth checking if your area was hit by a storm or fire.

The single highest-leverage habit is separation: move an estimated slice of every deposit — many operators use 25–30% of net profit — into a dedicated tax account the moment revenue hits. When the deadline arrives, the money is already sitting there, and none of the framework above ever has to come into play.