Income and self-employment tax on side income

Side Income Stacks on Top

A side hustle is taxed at the marginal rate — the rate applied to the last dollar earned — not the average rate across all income. A taxpayer already in the 22% federal bracket keeps a side gig's income taxed at 22% from the first dollar. This tool takes that marginal rate as an input so the estimate reflects the relevant bracket.

Self-Employment Adds a Separate Layer

Beyond income tax, most countries levy a self-employment or social-insurance charge on net earnings — a payroll-equivalent tax that salaried employees normally have split with their employer. Side-hustlers pay the full amount themselves. The combined bite (marginal income tax plus self-employment charge) frequently surprises new side-hustlers: a 22% income-tax earner adding a self-employment charge near 15% pays closer to 37% on the side income before any state or local tax. The tool takes both rates as inputs so the estimate fits your jurisdiction.

Quarterly Estimated Payments

Withholding from a day job covers the day-job's tax. Side income often requires quarterly estimated tax payments to avoid underpayment penalties. Saving the calculated tax reserve to a separate account and transferring to the tax agency each quarter keeps the process predictable.

A worked example

Try the defaults: annual side income of 15,000, marginal income tax rate of 22, self-employment tax rate of 15.3. The tool returns 5,595.00. You can adjust any input and the result updates as you type — no submit button, no reload. That's the real power here: seeing how sensitive the output is to one or two assumptions.

What moves the number most

The result responds to Annual Side Income, Marginal Income Tax Rate, and Self-Employment Tax Rate. Not every input has equal weight. Flip one at a time toward extreme values to feel which ones move the needle most for your situation.

The formula behind this

Income tax equals side income times marginal rate. Self-employment tax equals side income times SE rate. Total tax is the sum. Effective rate divides total tax by side income. Results are estimates for illustration purposes only. Everything the calculator does is shown in the formula box below, so you can check the math against your own spreadsheet if you want.

Why freelancers need this

Without a fixed salary, pricing decisions compound. A rate set too low today sets the ceiling for the next few years of clients. The calculation here makes the lifetime cost of underpricing visible — which usually changes the conversation with the next client.

What this doesn't capture

Freelance income is lumpy. The calculation assumes steady work; reality includes dry spells, delayed invoices, and client churn. Plan against a pessimistic version of the result, not the central case.