The deadline depends on how your business is structured. Not every entity type files on the same date, and getting them confused can result in penalties even if you’re only a few weeks late.

Partnerships (Form 1065) and S-Corporations (Form 1120-S) have a March 15 deadline. These are pass-through entities, meaning the income flows through to the individual owners’ personal returns. The earlier deadline exists so that owners receive their K-1 forms in time to file their own personal taxes by April 15.

Sole proprietors report business income on Schedule C as part of their personal tax return, so the deadline is April 15. C-Corporations (Form 1120) also file by April 15 for calendar-year filers. If your fiscal year ends on a date other than December 31, your deadline is the 15th day of the third or fourth month after your fiscal year ends, depending on entity type.

You can request an extension if you need more time. Partnerships and S-Corps get an automatic extension to September 15. Sole proprietors and C-Corps get until October 15. But here’s what catches a lot of business owners off guard: an extension to file is not an extension to pay. You still need to estimate what you owe and send payment by the original deadline. If you underpay, the IRS charges interest and penalties on the balance from the original due date.

When any of these dates fall on a weekend or federal holiday, the deadline moves to the next business day. Keep an eye on the calendar each year because this shifts things occasionally.

Beyond the annual return, many business owners also owe quarterly estimated tax payments. These are typically due April 15, June 15, September 15, and January 15 of the following year. If your business is profitable and you’re not withholding enough through payroll, skipping estimated payments leads to an underpayment penalty at year end.

One thing that simplifies life for Florida business owners is that there’s no state personal income tax. S-Corps, partnerships, and sole proprietors don’t have a separate state income tax return to worry about. C-Corporations in Florida do file a state corporate income tax return, but only if their taxable income exceeds the current exemption threshold.

If you’re behind or unsure about your filing obligations, getting your business tax returns handled professionally avoids the compounding penalties that come from missed deadlines. The cost of a late filing penalty on a partnership return alone is over $200 per partner per month.

The best approach is knowing your entity type, marking both filing and payment deadlines on your calendar, and working with someone who handles business tax preparation well before those dates arrive. Last-minute scrambles lead to errors, and errors lead to notices from the IRS that nobody wants to deal with.