The main federal form is Form 1120-S, the U.S. Income Tax Return for an S Corporation. This is due by March 15 each year for calendar-year filers. It reports the company’s income, deductions, credits, and other activity. The S-corp itself usually doesn’t pay federal income tax, but the return is still required. File it late and you’re looking at a $220 per shareholder per month penalty, which adds up fast.

Along with the 1120-S, you generate a Schedule K-1 for each shareholder. The K-1 shows each owner’s share of the business income, losses, deductions, and credits. That information flows onto your personal Form 1040, specifically Schedule E. This is where the income actually gets taxed. You pay taxes on your share of the profit whether or not you took a distribution, so staying on top of estimated payments matters.

In California, S-corps file Form 100S with the Franchise Tax Board. Unlike the federal return, California does impose a tax on S-corps. There’s a minimum $800 franchise tax plus a 1.5% tax on net income. This catches some business owners off guard because they assume S-corps don’t pay entity-level tax at all. California is different.

Since every S-corp must pay at least one shareholder a reasonable salary, payroll forms are unavoidable. Quarterly you file Form 941 with the IRS reporting wages paid and employment taxes withheld. Annually you file Form 940 for federal unemployment tax. You also issue W-2s to all employees and file them with the Social Security Administration along with Form W-3 by January 31. On the California side, you file DE-9 and DE-9C quarterly with the EDD.

If you pay subcontractors $600 or more during the year, you need to file 1099-NEC forms. For trade and construction businesses, this is a big one. Most contractors rely heavily on subs, and failing to issue 1099s can trigger penalties and raise red flags if you’re ever audited. These are due to recipients and the IRS by January 31 as well.

That’s a lot of deadlines and a lot of forms. Missing any of them creates penalties that stack up quickly. The 1120-S late filing penalty alone can reach thousands of dollars for a multi-owner S-corp. A CPA for construction businesses can keep all of these filings on track and make sure nothing slips through the cracks.

There are a few other forms that come up depending on your situation. If you make estimated tax payments (and most S-corp owners should), you use Form 1040-ES for federal and Form 540-ES for California. If you provide health insurance to a shareholder-employee who owns more than 2%, that gets reported on their W-2 in a specific way. And if the S-corp has depreciable assets like trucks and equipment, Form 4562 gets attached to the 1120-S.

The bottom line is that S-corp status creates real tax savings for most trade businesses, but it also creates real filing obligations. Keeping accurate books throughout the year makes business tax return preparation straightforward instead of a scramble. When your books are clean, your accountant isn’t guessing at numbers or chasing down missing information, and every deduction you’re entitled to actually makes it onto the return.