The Schedule C handbook

What Schedule C is

Schedule C ("Profit or Loss from Business") is the IRS form attached to your personal 1040 that calculates your business's net profit. If you're self-employed and not an S-corp, this is the most important tax form in your year.

The form has three main sections. Part I: income. Part II: expenses, broken into about 25 categories. Part III: cost of goods sold (only if you sell physical products). The bottom-line number — net profit — flows to your 1040 and gets taxed at your regular income tax rate plus the 15.3% self-employment tax.

You file one Schedule C per business. If you do freelance design and also sell pottery on Etsy, those are two separate businesses with two separate Schedule Cs. Don't bundle them.

Part I — Income (lines 1–7)

Line 1: gross receipts. The total of every dollar your customers paid you, before any refunds or fees. Includes Stripe deposits, Square deposits, checks, cash, ACH transfers, Venmo (if used for business), and 1099-NEC and 1099-K amounts.

Line 2: returns and allowances. Money you refunded to customers. Subtract from line 1.

Line 4: cost of goods sold (from Part III). Only physical-product businesses fill this in.

Line 6: other income. Bank interest on a business account, scrap sales, rebates from suppliers. Most service businesses leave this blank.

Line 7: gross income. The math of line 5 + line 6. This is what you have to work with before expenses.

Part II — Expenses (lines 8–27a)

This is where the deductions live. The IRS provides ~25 named categories and an "Other Expenses" bucket. Each category maps to a real-world cost: Advertising (line 8), Car & Truck (line 9), Contract Labor (line 11), Depreciation (line 13), Insurance (line 15), Interest (line 16), Legal & Professional (line 17), Office Expense (line 18), Rent (line 20), Repairs (line 21), Supplies (line 22), Taxes & Licenses (line 23), Travel & Meals (line 24), Utilities (line 25), Wages (line 26).

Clarity Books maps every transaction to its Schedule C line automatically based on the category you (or the AI) assigned. When you generate a Schedule C report, you see the exact line numbers and amounts ready to type into TurboTax or hand to your CPA.

The most-claimed lines for solo service businesses: Office Expense, Supplies, Software (under Office Expense or Other), Travel & Meals, Car & Truck (mileage), and Contract Labor (any 1099 contractors you paid).

Lines that get audited most often

Three categories trigger more IRS scrutiny than others. Knowing this means you should document them especially well — not avoid them.

Meals (line 24b): only 50% deductible (with rare 100% exceptions for staff events). The IRS wants to see a clear business purpose. Document: who you ate with, what business was discussed, the date, and the amount. A receipt with "lunch with Alex re: Q2 contract renewal" written on it is gold.

Car & Truck (line 9): mileage gets challenged because most people don't keep contemporary logs. The IRS specifically wants a log that was created at the time of each trip, not reconstructed at year-end. A mileage tracking app with timestamps is acceptable evidence; a spreadsheet you made up in March is not.

Home Office (line 30, separate from Part II): legitimate but requires "regular and exclusive use" of a defined space. A spare bedroom that doubles as a guest room does not qualify. A 100sqft corner of a room you use only for work does. The simplified method ($5/sqft, max 300sqft) is auditor-friendly.

The "Other Expenses" trap

Line 27a is a catch-all for expenses that don't fit the named categories. You list each one with its dollar amount on a continuation. It's the right home for things like Software/SaaS, Bank Fees, Education, Subscriptions, and Postage.

But: do not dump everything here. The IRS pattern-matches on returns where the named categories are mostly empty and "Other Expenses" is huge. It looks like you're hiding something. Use the named categories whenever there's a reasonable fit, and put genuinely-uncategorizable things in Other.

Clarity Books' Schedule C export distributes your transactions across the right named categories automatically and only uses Other when there's genuinely no better home.

Net profit, self-employment tax, and the math that matters

Line 31 is your net profit (or loss). This is the number that flows to two places.

First, your 1040 — added to your other income (W-2 wages, spouse's income, etc.) and taxed at your regular income tax bracket.

Second, Schedule SE, where you calculate self-employment tax: 15.3% on the first ~$168,600 (the 2026 Social Security wage base) and 2.9% on everything above that. This is in addition to regular income tax. You get to deduct half of the SE tax on your 1040, but it's still substantial.

Quick math: if your net profit is $80,000 and you're in the 22% federal bracket, your tax bill is roughly: $80,000 × 22% = $17,600 in income tax + $80,000 × 0.9235 × 15.3% = $11,300 in SE tax = $28,900 total federal tax. Plus state, if your state has an income tax. This is why setting aside 25–30% of net profit through the year matters so much.

When to do it yourself vs. hire a CPA

Do it yourself with TurboTax / FreeTaxUSA / TaxAct if: your business is one Schedule C, you didn't buy or sell major equipment this year, you don't have employees, and your gross income is under ~$200,000. Cost: $50–$150 in software.

Hire a CPA if: you have multiple businesses, multi-state income, you bought or sold a major asset (vehicle, equipment), you're considering an S-corp election, or you simply want a professional set of eyes on it. Cost: $400–$1,200 for a Schedule C and 1040 — usually worth it for the time saved and the deductions a pro will catch.

A clean year-end packet from Clarity Books cuts the CPA's prep time by 60–80%, which often translates to a smaller bill or faster turnaround.