The deadline depends on how your business is structured. For calendar year filers, which covers most small businesses, here are the key dates.

Sole proprietors file a Schedule C with their personal tax return, which is due April 15. Partnerships filing Form 1065 and S-corporations filing Form 1120-S are both due March 15. C-corporations filing Form 1120 are due April 15. If the deadline falls on a weekend or holiday, it shifts to the next business day.

California state returns generally follow the same deadlines. If you’re an LLC taxed as a partnership or S-corp, follow the March 15 federal deadline for both your federal and California returns.

You can file an extension if you need more time. Sole proprietors and C-corporations get until October 15. Partnerships and S-corporations get until September 15. Filing an extension is straightforward and doesn’t raise red flags with the IRS. But here’s the part that catches people off guard: an extension gives you more time to file, not more time to pay. If you owe taxes, the original deadline still applies. Interest and penalties start accumulating on any unpaid balance after that date, even if you filed a valid extension.

Late filing penalties are steeper than late payment penalties. If you owe money and don’t file or extend by the deadline, the failure-to-file penalty is 5% of unpaid taxes per month, up to 25%. The failure-to-pay penalty is much smaller at 0.5% per month. The takeaway is that filing an extension when you’re not ready is always better than missing the deadline entirely.

For partnerships and S-corps, there’s an additional penalty most owners don’t know about. Late filing triggers a penalty per partner or shareholder, per month late. Even if the business owes no tax, a two-partner LLC that’s three months late could face over $1,400 in penalties for what feels like a harmless delay.

The real challenge for most construction and trades businesses isn’t knowing the deadline. It’s having books that are ready when the deadline arrives. If your records are a mess in February, a March 15 deadline for your S-corp return becomes a scramble that leads to either a rushed filing or an extension followed by months of procrastination. Keeping your books current throughout the year means your CPA for construction businesses can prepare your return on time without guessing at numbers or chasing down missing records.

If you’re already behind, file the extension and use the extra time to get your books right rather than filing an inaccurate return. An accurate late return beats an inaccurate early one every time.