Small Business Tax Deadlines

For calendar-year filings made in 2026, partnerships and S corporations generally filed 2025 returns by March 16 because March 15 fell on Sunday, and individuals generally filed by April 15. The durable rules matter more than memorizing one year’s dates: Form 1065 and Form 1120-S are generally due on the 15th day of the third month after year-end; Form 1120 and individual returns are generally due on the 15th day of the fourth month, subject to corporate exceptions. Payroll deposits follow assigned schedules, while quarterly returns, annual wage and information forms, estimates, states, and special taxes have separate calendars.

This guide is part of Steady’s Business Taxes & the IRS library. It explains the federal workflow in practical terms, but the correct result still depends on the payment year, entity, worker relationship, filing method, and state rules.

The answer in context

Entity returns use different rules

Partnership and S corporation returns generally use the third-month rule, while individual and most C corporation returns use the fourth-month rule.

Extensions do not usually extend payment

Estimate the liability and pay by the original due date even when a valid extension provides more time to file.

Estimated payments have their own sequence

Individual estimates generally use the fourth, sixth, and ninth months and the first month after year-end; corporate estimates use their applicable calendar.

Payroll deposits are not quarterly by default

Monthly or semiweekly deposit schedules and the $100,000 next-day rule can require payment before Form 941 is due.

W-2 and 1099 deadlines differ by form and action

Furnishing, federal filing, states, corrections, and extensions can have different dates.

States and localities maintain separate calendars

Income, franchise, sales, payroll, paid leave, disability, local wage, annual report, and license dates can all apply.

Weekends, holidays, and disasters can shift dates

Use the current form instructions and official relief notices for the exact taxpayer and location.

An e-file acceptance is part of the deadline evidence

A prepared return is not filed, and a rejected submission needs timely correction under the applicable perfection rules.

Step-by-step workflow

1. Inventory every obligation. List tax, agency, account, form, period, frequency, owner, reviewer, payment, and proof.
2. Apply the entity’s tax year. Calculate due dates from the actual calendar, fiscal, short, start, or final year.
3. Load official dates. Use current IRS forms and Publication 509 plus each state’s official calendar.
4. Add internal cutoff dates. Set collection, close, review, authorization, and funding dates before the legal deadline.
5. Separate filing from payment. Create distinct tasks and evidence for extensions, returns, deposits, balances, and estimates.
6. Configure recurring payroll dates. Use deposit schedule, pay date, return frequency, year-end forms, and state or local requirements.
7. Monitor exceptions. Track weekends, legal holidays, disasters, address changes, acquisitions, new states, and agency notices.
8. Close every task with evidence. Save acceptance, certified mailing, payment confirmation, bank settlement, delivery, and reviewer sign-off.
9. Roll the calendar forward. After each filing, create the next period and update changed forms, thresholds, systems, and owners.

Worked example

A calendar-year S corporation with employees has no single tax day. It tracks payroll deposits during each month, quarterly Forms 941, state payroll filings, annual Form 940, W-2 and 1099 preparation and furnishing, the Form 1120-S and K-1 deadline under the third-month rule, shareholder estimates, state income and franchise filings, and an annual report. Each item has an internal collection date, approval date, legal due date, and proof field.

The example is intentionally a workflow illustration, not a conclusion for every taxpayer. A strong file connects each number on the return to a source report and records why an exception, exclusion, or classification was applied.

Records to keep

Keep the source form or worksheet, contracts or engagement records, payer and recipient identity support, the detailed payment or payroll ledger, bank and processor reconciliation, calculations, correspondence about corrections, filed copies, recipient-delivery evidence, and federal and state acceptance confirmations. Store the records by tax year and keep superseded versions when they explain a correction.

A reviewer should be able to begin with the final reported amount and trace it back to transactions without rebuilding the year. Add a short review memo for judgments such as worker status, corporate exemption, payment-method exclusion, state filing, or unusual timing. That memo is often more useful than another unlabeled spreadsheet.

Common mistakes

• Using April 15 for every business. Entity, payroll, information, state, and excise deadlines differ.
• Calendaring returns but not deposits. Payroll and other deposits may be due well before the related return.
• Assuming an extension covers tax due. Create a separate payment estimate and confirmation.
• Copying last year’s dates. Weekends, holidays, law, systems, and disaster relief change exact dates.
• Scheduling only the legal deadline. Add earlier book-close, document, review, authorization, and cash deadlines.
• Ignoring rejection messages. Monitor federal and state acceptance and correct promptly.
• Leaving the calendar with one person. Use a shared register with preparer, reviewer, backup, and escalation.

Final review before filing

Confirm the form and revision year, taxpayer identities, dollar fields, payment categories, withholding, filing channel, recipient statement, state obligations, due dates, and approval. Compare the final output with the source reconciliation rather than reviewing the form in isolation. If software recalculates an amount after an edit, rerun the tie-out.

Keep preparation, filing, and acceptance as three separate statuses. A draft can be complete but unfiled; a transmission can be sent but rejected; a federal return can be accepted while a state return is still missing. This status discipline prevents a polished PDF from being mistaken for finished compliance work.

How to handle a discrepancy

When a source form, ledger, payroll report, or software preview disagrees with another record, stop before filing and identify which amount represents the underlying transactions. Trace the difference by vendor or employee, date, invoice or payroll run, payment channel, and account. Common causes include a payment posted to the wrong year, a void recorded after a report was generated, a card payment included with checks, a duplicate import, an incorrect taxpayer name, or a late adjustment. Record the explanation and the correcting entry or form request.

Do not erase the trail by overwriting the original report. Save the first version, the reconciliation, the corrected version, and the approval. If a third party supplied an incorrect information return, request a formal correction and retain the correspondence. If a return was already transmitted, use the current correction procedure for that form and channel. A corrected recipient copy without a corresponding agency correction can leave the records inconsistent.

Federal filing is only one layer

Federal acceptance does not settle state or local obligations. A state may use a different threshold, worker test, filing portal, account number, transmittal, or due date. Some states receive eligible information through a combined program, while others require a direct submission. Verify the jurisdictions connected with the payer, recipient, employee, work location, withholding, and business activity. Save state confirmations separately so they are not hidden behind the federal acceptance.

Make next year easier

Turn the year-end work into a monthly control. Collect identity forms during onboarding, code payment methods consistently, reconcile payroll and vendor activity each month, and flag vendors or income streams that need special treatment. Schedule a fall review of missing forms, classification questions, state registrations, and electronic-filing access. By year-end, the team should be validating a maintained file instead of reconstructing twelve months of transactions under a deadline.

Practical implementation notes

Calendar fields

Track obligation, period, due date, internal date, amount, status, acceptance, payment, owner, and reviewer.

Source date

Record the official page or instruction revision used for each deadline.

Cash forecast

Link deposits, estimates, and balances to the operating forecast before funds are needed.

Exception log

Document extensions, holidays, disasters, notices, waivers, and corrected submissions.

Deeper planning points

2026 filing reference

Distinguish filing year from tax year. A deadline occurring in 2026 often concerns 2025 income, while 2026 estimated payments concern the current year and the January 2027 installment. Label every task with form and tax period.

Fiscal and short years

Calculate rather than copy calendar dates. Formation, termination, election changes, mergers, and accounting-period changes can create short returns. Use the governing form instructions for the actual year-end and any special rule.

For the next layer of context, see this related guide, the companion reporting article, and the connected workflow.

If the form, books, and filing status do not agree, Steady can help reconcile the source data and prepare a clean filing package through its specialist service.