The single most common reason a small business misses a deadline is not knowing which one applies to its entity type. Individual returns, corporate returns, and partnership returns are not all due on the same date, and the gap between them catches people who assume "tax day" means one thing.
| Entity type | Typical federal filing deadline |
|---|---|
| Sole proprietor (Schedule C) | Filed with your individual return, generally 15 April |
| Partnerships and multi-member LLCs taxed as partnerships | Generally 15 March |
| S-corporations | Generally 15 March |
| C-corporations | Generally 15 April (calendar-year corporations) |
It does not stop at one date a year
A business with employees or estimated tax obligations is not dealing with a single annual deadline at all. Quarterly estimated tax payments run on their own schedule, and payroll tax deposits run on a schedule set by your deposit frequency, which can be as often as every payday. See the guide on payroll tax basics for what that involves.
Extensions
Nearly every one of these returns can be extended, typically for six months. An extension buys time to file the paperwork correctly; it does not extend the time to pay what is owed. Estimate and pay by the original deadline even if the return itself is going to be late.