Side income and taxes: what a first-year earner should know

Employee pay and side income are taxed differently

On a regular paycheck, your employer withholds income tax and your share of Social Security and Medicare, then pays a matching employer share. When you work for yourself, you handle both halves. The IRS describes self-employment tax as Social Security and Medicare taxes "primarily for individuals who work for themselves," calculated on Schedule SE.

That is why side income can feel more heavily taxed than the same amount of salary. The money is the same; the paperwork and the timing are now yours.

The self-employment tax basics

According to the IRS self-employment tax page:

• The self-employment tax rate is 15.3% (2026 tax year), made up of 12.4% for Social Security and 2.9% for Medicare.
• You must pay self-employment tax and file Schedule SE if your net earnings from self-employment were $400 or more (2026 tax year; special rules apply to church employee income).
• For the 2026 tax year, the Social Security part applies only to the first $184,500 (2026 figure) of combined wages, tips and net self-employment earnings. If your wages already reached that amount, the 12.4% part does not apply to your self-employment earnings, but the Medicare part still does.
• You can deduct the employer-equivalent portion of self-employment tax when figuring adjusted gross income. That deduction affects income tax, not the self-employment tax itself.

Two words in those rules matter a lot: net earnings. Self-employment tax is figured on profit, not on gross receipts. Platform fees, supplies used for the job and other ordinary business expenses generally reduce the amount the tax applies to, which is one reason records matter so much.

The IRS also notes that these rules apply "no matter how old you are," including to people already receiving Social Security or Medicare.

Income tax still applies on top

Self-employment tax is separate from income tax. Your side profit is added to your other income, and income tax is figured on the total after deductions. That means the rate on your side income depends on your whole situation: your salary, filing status, deductions and credits. Nobody can give you a single correct percentage without looking at the full return.

A practical approach for a first year is to treat your reserve as a range rather than one exact figure. The tax cash reserve workbench lets you choose your own percentage and see what that means for each payment. It does not calculate a tax bill; it helps you hold cash aside so the bill, whatever it turns out to be, can be paid.

When estimated payments come into it

The tax system is pay-as-you-go. The IRS estimated tax page says individuals, including sole proprietors, "generally have to make estimated tax payments if they expect to owe tax of $1,000 or more when their return is filed." (IRS estimated tax page as checked for the 2026 tax year) The year is divided into four payment periods, each with its own due date, and you can be charged a penalty for paying too little or too late, even if you end up due a refund.

There are some useful details on that same page:

• If you also have a job, you can often avoid separate estimated payments by asking your employer to withhold more, using a new Form W-4. The IRS Tax Withholding Estimator helps with this.
• You may pay more often than quarterly, for example monthly, as long as enough is paid by the end of each period.
• Most taxpayers avoid the underpayment penalty if they owe less than $1,000 after withholding and credits, or paid at least 90% of the current year's tax or 100% of the prior year's tax (2026 tax year rules), whichever is smaller. Higher-income taxpayers and some other groups have special rules described in Publication 505.

The exact quarterly due dates are printed on Form 1040-ES for each year, and they shift when a date falls on a weekend or holiday. Look them up for the current year rather than relying on memory.

Forms you might receive

Clients and platforms may send you information returns. A business that pays you for services may send a Form 1099-NEC; payment apps and marketplaces may send a Form 1099-K. The thresholds for when these forms must be sent have changed recently, and our separate note on 1099 forms covers the details. The key point for this page: the IRS is clear that you must report all income from selling goods or services whether or not a form arrives.

Records that make the return easier

Good records do two jobs. They help you claim the expenses you are entitled to, and they help you answer questions if the IRS ever asks. For a small side income, a simple routine is enough:

1. Record every payment received, including the platform and any fee deducted before payout.
2. Save receipts for supplies, software, equipment and other costs connected to the work.
3. If you drive for the work, keep a mileage log written at the time of the trip. Our note on vehicle costs and mileage explains why.
4. Keep personal and business money apart where you can, even if that just means one separate account.

How long to keep them depends on the situation. The IRS records page says to keep records for 3 years in the ordinary case (IRS guidance as checked for the 2026 tax year), with longer periods in specific situations, such as 6 years if you leave out income that is more than 25% of the gross income shown on your return. Keep copies of filed returns too.

A sensible first-year routine

• Every payment: log it and move your chosen reserve percentage into a separate savings account.
• Every month: total income and expenses, and compare the reserve with what your rough estimate says you might owe.
• Before each estimated tax due date: decide whether a payment is needed or whether extra withholding at your job covers it.
• At year end: gather 1099 forms, compare them with your ledger, and note any differences before you file.

When to get help

Consider a qualified tax professional if you have income from several sources, sell physical inventory, use part of your home for the work, hire help, or are unsure whether you are an employee or a contractor for a particular client. The IRS also offers free resources and filing help for eligible taxpayers. This fieldbook explains how the pieces fit; it cannot prepare your return or tell you what you owe.