The Sole Proprietor's Tax Deadline Playbook: Schedule C Deductions You're Probably Missing

If you're self-employed, your tax return is more complex than a W-2 filer's — and every deduction you miss comes straight out of your pocket. This playbook walks through the Schedule C deductions sole proprietors overlook most often, plus the deadlines and safe harbors that keep penalties away.

Start with the number that shocks everyone: self-employment tax

Before deductions, know the headline: net earnings from self-employment are hit with 15.3% self-employment tax (12.4% Social Security plus 2.9% Medicare) on 92.35% of your net profit. The good news: one-half of it is deductible above the line, and it applies to net profit — which means every legitimate deduction does double duty, cutting both income tax and SE tax.

The home office: two ways to claim it

If you use part of your home exclusively and regularly for business, you have two methods. The simplified method: $5 per square foot, up to 300 square feet — a $1,500 maximum deduction, no depreciation recapture when you sell the home. The actual-expense method: a pro-rata share of mortgage interest or rent, utilities, and insurance — usually the bigger deduction, but it demands real records and triggers depreciation recapture later. Pick the method with math, not habit.

Your car: the 70-cent question

For 2025, the IRS business standard mileage rate is 70 cents per mile. Standard mileage usually wins for moderate-mileage drivers and asks only for a log: date, miles, business purpose. Actual expenses can win for expensive vehicles driven heavily — but you must track everything, and you can't flip methods freely year to year. Either way, the rule is absolute: no log, no deduction.

Estimated taxes: the safe harbors that prevent penalties

You generally avoid underpayment penalties if your withholding and quarterly estimates cover 100% of last year's total tax — 110% if last year's adjusted gross income topped $150,000 — or 90% of this year's tax. And if you owe less than $1,000 after withholding and credits, there's no penalty at all. When I prepare a Schedule C, I always reset next year's estimates at the same time.

Don't forget the 20% QBI deduction

Section 199A allows up to 20% of qualified business income as a deduction for many sole proprietorships. Taxable-income thresholds and phase-ins apply, and specified service businesses face tighter limits at higher incomes — so confirm it on the return rather than assuming it.

2025 law changes working in your favor

Recent legislation restored 100% bonus depreciation for qualified property acquired after January 19, 2025, and raised the Section 179 expensing limit to $2,500,000. If you bought equipment, vehicles, or technology for the business this year, the first-year write-off picture is the best it's been in years.

No receipts? Don't panic — reconstruct

Bank and credit card statements are a legitimate starting point. Courts allow reasonable reconstructed estimates where some factual basis exists — but mileage and a handful of other categories have strict substantiation rules with no wiggle room. Send a CPA everything; sorting what's defensible is literally the job.

A final note

General guidance only. This article provides general tax information and is not tax advice for your specific situation. Tax law changes frequently — consult a qualified CPA about your facts before acting.

Veltriqa LLC — US tax return preparation, audit and assurance, SOC 2 readiness, and advisory services for individuals and businesses.