Side Project LLC Taxes While Working Full Time

No separate federal return unless you elect corporate status. Report income and expenses on Schedule C attached to Form 1040. Net profit is subject to income tax plus self-employment tax (15.3% on net earnings up to the Social Security wage base, then 2.9% Medicare).

Your W-2 job already covers Social Security up to the wage base. Side project profit still pays SE tax — but you get a deduction for the employer-equivalent portion on your 1040.

Open a dedicated business checking account. Pay side-project expenses from it. Transfer a 'salary' to personal monthly if you want, but keep clean records for Schedule C line items.

Side income has no withholding. If you'll owe $1,000+ after W-2 withholding, pay estimated taxes via Form 1040-ES in April, June, September, and January.

A common shortcut: increase W-4 withholding at your day job to cover side income. Easier cash flow than separate ES payments, but only works if your HR system allows enough extra withholding.

Underpayment penalties hit people who had a big Stripe year and only one W-2 job with steady withholding. Set aside 25–35% of side profit if you're in a high-tax state until you know your real rate.

If the activity isn't conducted for profit, the IRS can treat it as a hobby under Section 183. You still report the income, but hobby expenses are generally nondeductible under current law — not merely limited miscellaneous deductions.

Profit in three of five years is a safe harbor for presuming profit motive. Document business plans, marketing spend, time logs, and separate accounts to support deductibility if you're still in the red.

Writing off a 'side project' that's mostly personal learning with no revenue is a audit magnet. Losses need a plausible path to profit.

Electing S corp (Form 2553) can reduce self-employment tax if net profit is well above a reasonable salary — you pay SE tax on W-2 from the S corp, not on all distributions. Filing Form 1120-S and running payroll has costs.

Rough rule of thumb: S corp often gets discussed around $60K–$80K+ in consistent net profit. Below that, Schedule C simplicity usually wins.

Electing S corp for a side LLC while keeping a full-time W-2 is doable but adds March 15 S corp deadlines and payroll compliance. Miss an 1120-S deadline and you pay penalties on a side hustle.

☐ Schedule C on Form 1040 (default LLC)

☐ Schedule SE for self-employment tax on side net profit

☐ Form 1040-ES quarterly if not increasing W-4 withholding

☐ 1099-K from Stripe/PayPal if thresholds met; 1099-NEC to contractors you pay $600+

☐ State LLC annual report and fees (varies by state — don't forget these)

☐ Sales tax registration if you sell physical goods or SaaS in nexus states

☐ Form 2553 only if S corp election makes sense — 75-day deadline from formation or tax year start

Run the numbers on 3–6 months of side revenue, not one good month. Your full-time job is covering health insurance and steady withholding — replacing both has a tax cost.

If you're approaching contractor-to-founder territory, wind down the side LLC cleanly or convert it into the new C corp with counsel — don't leave two overlapping entities.

Check your employment agreement for IP assignment and outside-business clauses. Tax planning doesn't help if the side project belongs to your employer legally.