Internal Revenue Code (IRC) Guide for Small Businesses
Plain-English map of the Internal Revenue Code for small business owners: entity types, who is covered, 21% and 20% rates, deadlines and penalties, with slides.
Last reviewed October 29, 2026 · General information, not legal advice
General information only, not legal advice. CPA Tax Payroll and Accounting Corp is a CPA firm, not a law firm. Laws change: confirm with the official source or a licensed attorney before you act. Read the full notice.
The Internal Revenue Code (IRC) is Title 26 of the U.S. Code, the federal tax law run by the Internal Revenue Service (IRS). It is far too large to read, so this page is a guided map of the parts a small business meets: how the business is classified, which accounting method it uses, what it can deduct, what it reports and what happens when it falls behind. It is for owners, freelancers, nonprofit leaders and professionals who want to know where to look next.
Slide show: The Internal Revenue Code in seven slides
What the Code does
It decides how each kind of business is taxed: sole proprietor or LLC by default, partnership, S corporation or C corporation.
Who it covers
Every business owner. The entity type comes from default rules or from an election on Form 8832 or Form 2553.
The rule
C corporations pay 21 percent. Owners of pass-through businesses may deduct up to 20 percent of qualified business income, now permanent.
The number
The 2026 Section 179 limit is $2,560,000. Bonus depreciation is 100 percent for qualifying property acquired after January 19, 2025.
The deadline
An S election is due within 2 months and 15 days after the tax year starts. Returns are due on the 15th day of the third month after year end for partnerships and S corporations, the fourth for C corporations.
The penalty
Accuracy errors cost 20 percent of the underpayment, and fraud 75 percent of the part due to fraud. A late return costs 5 percent of the unpaid tax per month, up to 25 percent.
A tip
Keep records at least 3 years, 6 if you may have left out over 25 percent of income, and 4 for payroll. Page 3 turns this into the Seven-Lantern Tax Trail.
Income passes through. Up to 100 shareholders; individuals, estates, certain trusts and certain exempt organizations only; no nonresident alien shareholder; one class of stock
Form 2553
Cash method of accounting
C corporations, and partnerships with a C corporation partner, need 3-year average gross receipts of $32 million or less (2026); farming and qualified personal service corporations are exempt
n/a
How it touches your taxes and payroll
The entity drives payroll tax. Earnings of sole proprietors, partners and LLC members taxed as such generally bear self-employment tax. Wages paid to an S corporation owner who works in the business carry FICA payroll taxes, and the IRS can reclassify pay labeled as distributions into wages. Worker status decides whether a payment goes on Form W-2 or Form 1099-NEC; see employee vs. independent contractor.
