After 30 years as a CPA, I've reviewed thousands of small business tax returns. The same mistakes show up over and over — and they cost business owners real money.

Here are 5 deductions I see missed constantly:

1. Home Office (the right way) — Most people either skip it entirely or calculate it wrong. If you use a dedicated space for business, you can deduct a proportional share of rent/mortgage, utilities, insurance, and repairs. The simplified method gives you $5/sq ft up to 300 sq ft, but the actual expense method often yields more.

2. Vehicle Expenses — You drove to meet a client, pick up supplies, or attend a conference? That's deductible. The 2026 standard mileage rate adds up fast. Keep a mileage log (even a simple app works).

3. Health Insurance Premiums — If you're self-employed and not eligible for a spouse's employer plan, your premiums are deductible above the line. This includes dental and long-term care.

4. Retirement Contributions — A SEP-IRA lets you contribute up to 25% of net self-employment income. That's potentially $69,000+ off your taxable income.

5. Education & Professional Development — Courses, books, conferences, coaching — if it improves skills you use in your business, it's likely deductible.

The difference between a $50K tax bill and a $45K tax bill is knowing what to look for. Most business owners don't have the time to track every change in tax law — that's exactly why I built Tax CoPilot.