US Business Tax Preparation: Returns, Deadlines and Records

Business tax preparation in the US starts with one question: how is your business taxed? The answer decides which federal return you file, when it is due, and how profit reaches the owners. This guide walks through each common structure, the 2026 filing calendar for tax year 2025, what preparation actually involves, and how to get your records ready.

This is general information, not advice for your business. Confirm current rules with the IRS sources at the end.

Which federal return does your business file?

How the business is taxed	Federal return	Who pays the income tax	Calendar-year due date (tax year 2025)
Sole proprietor or single-member LLC owned by a US person	Schedule C attached to the owner's Form 1040	The owner	April 15, 2026
Single-member LLC owned by a foreign person	Form 5472 with a pro forma Form 1120	Usually informational only	April 15, 2026
Partnership or multi-member LLC (calendar year)	Form 1065, with a Schedule K-1 for each partner	The partners	March 16, 2026
S Corporation, calendar year (corporation or LLC with an S election)	Form 1120-S, with a Schedule K-1 for each shareholder	The shareholders, in most cases	March 16, 2026
C Corporation (or LLC electing corporate tax)	Form 1120	The corporation, at the 21% federal rate	April 15, 2026

March 15, 2026 falls on a Sunday, so partnership and S corporation returns are due the next business day. Fiscal-year businesses use different dates.

An LLC has no tax classification of its own. It is taxed as a sole proprietorship, partnership, S corporation or C corporation depending on its members and any election filed on Form 8832 or Form 2553.

Extensions

Form 7004 gives an automatic six-month extension to file Forms 1120, 1120-S and 1065. For tax year 2025, that moves partnership and S corporation returns to September 15, 2026, and C corporation returns to October 15, 2026. An extension does not extend the time to pay any tax due.

Late filing penalties for partnerships and S corporations are calculated per partner or shareholder per month, so a late K-1 return can be expensive even when no tax is owed by the entity.

What business tax preparation actually involves

A good preparer does more than enter totals into software. A typical engagement includes:

Reviewing the books. Confirming that bank and card accounts reconcile, that owner draws are separated from expenses, and that income is complete.
Converting book income to taxable income. Adjusting for items such as meals, depreciation, owner health insurance and non-deductible penalties.
Depreciation and asset elections. Deciding how equipment, vehicles and improvements are depreciated, including any Section 179 or bonus depreciation election.
Owner reporting. Preparing accurate Schedule K-1s and checking basis, distributions and, for S corporations, that owner-employees receive reasonable compensation through payroll.
State returns. Filing in every state where the business has nexus, which can come from property, payroll, sales or physical presence.
Review and filing. A second review before e-filing, then confirmation that each return was accepted.

Related filings that are easy to miss

Information returns. Form 1099-NEC is generally due to contractors and the IRS by January 31.
Estimated taxes. C corporations that expect to owe $500 or more generally make quarterly estimated payments. Owners of pass-through businesses often make individual estimates. See our guide to calculating US quarterly estimated taxes.
Payroll returns. Forms 941 and 940, and W-2s to employees.
State franchise and annual report filings. Delaware, California and Texas, for example, each have their own annual obligations separate from income tax.
Foreign owner reporting. Corporations that are at least 25% foreign owned may also need Form 5472.

Deductions worth checking every year

Ordinary and necessary business expenses are generally deductible. Common categories include rent, software, contractor costs, professional fees, business insurance, a share of home office costs where the rules are met, and business travel. Our guide to deductible business expenses covers these in more detail. Keep receipts and records; a deduction you cannot support may be disallowed on audit.

Document checklist

Prior-year federal and state returns
Year-end bank, card and loan statements
Profit and loss statement and balance sheet
Fixed asset purchases and disposals
Payroll reports and W-2/W-3 summaries
Forms 1099 issued and received
Ownership changes, capital contributions and distributions
Any IRS or state notices received during the year

Common questions

Is an LLC tax return different from a corporate return? It depends on the election. A multi-member LLC files Form 1065 by default, a single-member LLC owned by a US person uses Schedule C, and an LLC that elected S or C corporation status files Form 1120-S or Form 1120.

Can I file my business return myself? You can. Many owners hire a preparer once there are multiple owners, payroll, several states or foreign ownership, because the related schedules and elections get more complex.

What if I missed a prior year? File it as soon as possible. Penalties and interest generally keep growing until the return is filed. If the IRS is already collecting a balance, our guide to resolving IRS tax debt explains the options.

How Gullia Filing helps

We prepare Forms 1120, 1120-S, 1065, Schedule C and the related state returns, with a review before every filing. Learn more about our business tax preparation services. We do not promise a particular tax saving or refund, and we tell you the fee before work begins.