Manage Financial Side Business as Sole Proprietor: Your 2026 Tax Playbook

When you manage a financial side business as sole proprietor, the single best defense you have isn't a clever deduction — it's a clean ledger. Scott Singer proved that. He ran an RV-repair and installation company as its sole owner, and over three years he lent his struggling business $646,443. He booked every advance as a shareholder loan on both his ledger and his tax returns. When the company later paid $181,872 of his personal expenses and the IRS called it disguised wages, the Tax Court sided with Singer. His books told the same story every year, consistently and contemporaneously, so the payments were loan repayments — not compensation. The IRS formally acquiesced in the result (AOD 2017-04).

Here's the nuance that matters to you: advances Singer made during profitable years counted as loans. Advances during loss years were held to be capital contributions. The win was partial, and the nuance is the lesson. Owners win these fights when the bookkeeping tells the same story every year — documented at the time, not reconstructed at tax time.

That principle is the foundation for everything below. Whether you're an HVAC tech pulling side jobs, a landscaper building a client base on weekends, or a plumber transitioning from company man to your own boss, the mechanics here are what keep your money straight and your tax bill defensible. For the full contractor planning picture, our contractor tax planning hub lays out the broader strategy.

What taxes does a sole proprietor pay?

A sole proprietor pays two layers of tax on business profit: self-employment tax and income tax. Self-employment tax is the Social Security and Medicare tax you pay on business profit — both halves, because you're the employer and the employee. The rate is 15.3% on net earnings up to the 2026 Social Security wage base of $184,500 (SSA 2026 fact sheet). Above that line, you pay 2.9% on the rest. There's no employer splitting the bill with you.

On top of SE tax, your business profit flows onto your personal return and gets taxed at your individual income tax rates. A sole proprietorship is a pass-through — the business itself pays no income tax; the profit lands on your personal return instead. You report everything on Schedule C. For a deeper dive on the calculation, our guide to self-employment tax for contractors breaks it down line by line.

How much should I set aside for taxes from my side business?

Our standing advice to trade contractors: sweep 25 to 30 cents of every net dollar into a separate tax account the day you take the draw. In a no-income-tax state, 25% of net business income covers federal SE tax and income tax for most filers. In California, use 30% — the state adds income tax and a 1.3% SDI charge with no wage ceiling. In an unusually profitable year, push to 35% or higher.

Always apply this to net income, never gross. If a plumbing job pays $5,000 and your materials and subs cost $2,000, your net is $3,000. Set aside 25% of $3,000, which is $750. That $750 goes into a separate account the moment the check clears — not at the end of the quarter when the payment is due. For the full breakdown on reserve targets, see our guide on how much to set aside for taxes.

When do I pay taxes, and how?

You pay four times a year through estimated taxes. The 2026 due dates are April 15, June 15, September 15, and January 15 of the following year. Each payment covers both your income tax and your self-employment tax for that quarter.

The safest approach is the safe harbor. Pay 100% of your prior-year total tax and you're protected. If your adjusted gross income was over $150,000, the target rises to 110% of prior-year tax. Either way, hitting the target shields you from the underpayment penalty.

Our guide on how to pay quarterly taxes walks through the payment methods and calculation in detail.

What can I deduct as a sole proprietor?

Any expense that is ordinary and necessary for the work is deductible. Materials, tools, vehicle costs, insurance, advertising, subcontractor payments, and a home office all qualify if they're genuinely for the business.

Big purchases get special treatment. Section 179 lets you write off up to $2,560,000 of qualifying equipment in 2026 in full the year it goes to work, instead of depreciating it over years. Bonus depreciation is back at 100% for 2026 for assets placed in service after January 19, 2025. A new $8,000 compressor for your HVAC van can go straight to the bottom line the year you buy it.

Vehicle costs are one of the most common deductions contractors miss or misreport. The IRS treats vehicles as listed property, which means it demands stricter records. A mileage log is the defense. Our contractor vehicle tax deduction guide covers the standard mileage vs. actual cost choice, and our broader tax write-offs for contractors checklist covers everything else.

Does the QBI deduction apply to my sole proprietorship?

Yes. QBI, the qualified business income deduction, shields up to 20% of your business profit from income tax, with limits at higher incomes. For 2026, the full deduction phases out starting at $201,750 of taxable income for single filers. For married filing jointly, the phase-out starts at $403,500. Below those lines, you get the full 20% off your net business profit.

The deduction also has a minimum floor for 2026. If you have at least $1,000 of qualified business income, the deduction is at least $400. The rate stays 20%. This is a deduction against income tax — it does not reduce your self-employment tax. But on the income tax side, it's real money. If your Schedule C nets $80,000 and you're in the 22% bracket, the QBI deduction of $16,000 saves you $3,520 in income tax.

When should I stop being a sole proprietor and switch to an S-Corp?

Our threshold: when net profit clears $80,000 to $100,000 and looks repeatable, it's time to run the S-Corp math. Below that, payroll costs, tax-prep fees, and state compliance eat the savings. Above it, the savings grow faster than the fixed costs.

The savings come from self-employment tax. An S-Corp isn't a different kind of company; it's a tax status you elect. Instead of paying 15.3% SE tax on all profit, you pay yourself W-2 wages and take the rest as distributions. Distributions don't carry SE tax.

Wages are subject to FICA. In our experience representing contractors in audits, a salary of roughly one-third of net profit is the level that consistently holds up as reasonable compensation. The remaining two-thirds comes out as distributions free of the 15.3% SE tax.

On $100,000 of net profit, that's roughly $33,333 in wages. The remaining $66,667 comes out as distributions. The SE tax savings on that distribution portion is about $10,200. You make the switch by filing Form 2553. For the full comparison, see our breakdown of LLC vs S-Corp for contractors and our guide on when the S-Corp election starts making sense.

What records do I need to keep to protect myself?

Go back to Scott Singer. He won his case because his ledger told the same story every year. Advances were labeled as loans when they happened. Repayments were tracked. The books were consistent between the company ledger and the tax returns. That's what made the Tax Court believe him.

For a sole proprietor, the practical version is simpler but the principle is identical. Keep a separate business bank account — every dollar in and out flows through it. Run reconciliation at least monthly, matching your books against the bank statement until they agree. Maintain a chart of accounts that separates materials, labor, vehicle, tools, and office expenses. Save receipts for anything you deduct. Log your miles if you're claiming vehicle expenses.

The statute of limitations means you need records going back at least three years, the IRS's usual deadline to audit a return. But clean books are about more than surviving an audit. They're about knowing your real numbers so you can price jobs, manage cash, and make the entity decision at the right time.

Can I open a retirement account as a sole proprietor?

Yes, and it's one of the best tax moves available. A SEP-IRA lets you contribute up to $72,000 in 2026. That's capped at 25% of your compensation, whichever is less. A Solo 401(k) lets you put in $24,500 as an employee deferral. You can add up to 25% of compensation as an employer profit-sharing contribution on top of that, with a total cap of $72,000 for 2026.

If you're 50 or older, the Solo 401(k) adds an $8,000 catch-up contribution. Ages 60 through 63 get a super catch-up of $11,250. Every dollar you put in reduces your taxable income for the year, and the growth is tax-deferred until you withdraw it. For the head-to-head comparison, see our guide on SEP-IRA vs Solo 401(k) for self-employed contractors.

What should I do first to get my side business finances in order?

Open a separate business checking account today. Run every business dollar through it. Start tracking mileage if you use a vehicle for work. Set up a separate savings account for tax reserves and sweep 25% to 30% of every net dollar into it the day the payment clears. Get a W-9 from any subcontractor you pay — it gives you the legal name and tax ID you'll need at 1099 time.

Whatever story your money tells — loans in, draws out, repayments — make the ledger tell it the same way every year, and label it at the time, not at tax time. That's what Scott Singer did, and it's the one thing entirely in your control.

Ready to get a second opinion on your side business tax setup? Book a meeting with our team and we'll walk through your numbers together.