How to Track Side Income and Set Money Aside for Taxes

Side income from reselling, gig apps, tutoring, or small online sales adds up quickly, and so does the tax bill if you aren't ready for it. A simple tracking system keeps your records clean, shows what's actually profitable, and helps you set money aside so tax time isn't a shock. This guide covers the tracking and points you to the official IRS rules. It's general information, not tax advice.

Why tracking matters

• Taxes: In the U.S., income is generally taxable whether or not you receive a form for it. The IRS explains this on its gig economy tax page.
• Profit: Platform fees, shipping, and supplies can quietly eat most of a sale. Tracking shows what you really keep.
• Planning: Seeing income by month helps you budget around uneven earnings.

The columns you need

Keep one row per payment or payout:

• Date
• Source (platform, client, or activity)
• Gross amount received
• Fees (platform, payment processing, shipping)
• Net amount (gross − fees)
• Notes (what it was for)

Keep a second list for expenses that aren't tied to a single sale, like supplies or equipment, with date, description, and amount. Save receipts, digital or paper.

The official tax basics to know

These are well-established IRS rules. Always check the IRS pages for current details:

• Self-employment tax. If you have net earnings from self-employment of $400 or more, you generally must pay self-employment tax, which covers Social Security and Medicare. The rate is 15.3% (12.4% Social Security and 2.9% Medicare) on net earnings, with details and limits on the IRS's self-employment tax page. This is in addition to regular income tax.
• Estimated taxes. If you expect to owe enough tax that isn't withheld, you may need to make quarterly estimated payments using Form 1040-ES. The IRS lists the due dates and rules on its estimated taxes page. The usual quarterly dates are around April 15, June 15, September 15, and January 15 of the next year (dates shift for weekends and holidays).
• Business expenses. Ordinary and necessary expenses for your side business may be deductible, which lowers your net earnings. Keep records.
• Forms. You may receive Form 1099-NEC or 1099-K from clients or platforms, but income is reportable even if you don't get one.

How much to set aside

There's no single right percentage because it depends on your total income, deductions, and state. Many people use a rough rule of thumb, like 25% to 30% of net side income, as a starting place, and then adjust once they see their actual tax return. Treat any percentage as a rough guide only. A tax professional or the IRS's free resources can help you refine it. If your employer withholds taxes from your main job, another option is to increase your W-4 withholding to cover the side income; the IRS has a Tax Withholding Estimator for that.

Make set-asides automatic

• Open a separate savings account just for taxes.
• Each time a side payment arrives, move your chosen percentage of the net amount right away.
• Pay estimated taxes from that account when they're due.
• Don't count tax money as savings for other goals. It's already spoken for.

A worked example (illustration only)

Over three months, $1,330 gross became $1,148 net, and $287 went to the tax account. These are made-up numbers to show the math.

Free: Paycheck Budget Lite

A simple starter spreadsheet for Google Sheets or Excel. List your take-home pay and bills and see what each paycheck has left. Free, instant download.

Download the free template

Track by source to see what's worth it

Add up net income per source each month. You may find one activity brings in most of your profit for a fraction of the time. Consider net per hour, too: a gig that pays more gross might pay less once fees and mileage are counted.

Budget side income carefully

Side income is often irregular. A safe approach is to budget your bills on your main paycheck only, then give side income specific jobs: taxes first, then a goal like debt payoff or your emergency fund. That way a slow month doesn't break your budget.

Records to keep

• Your income log and expense list
• Receipts and invoices
• Platform statements and 1099 forms
• Mileage logs if you drive for side work (the IRS explains vehicle expense rules in Publication 463)

The IRS generally recommends keeping records for at least as long as the period during which a return can be examined; see its record-keeping guidance.

A tool to make it easy

Our Side Income Tracker logs income by source and month, subtracts fees, and shows a suggested tax set-aside at a percentage you choose (default 25%, a rough guide only). It works in Google Sheets, Excel, and LibreOffice.

The bottom line

Log every payment, subtract fees, move a set-aside to a separate tax account the same day, and check the official IRS pages for rules and due dates. Clean records and a steady set-aside turn tax season from a surprise into a formality.

A simple monthly side-income routine

• At the end of each month, download payout reports from each platform.
• Check that every payout is in your log, with fees separated.
• Add any business expenses and file the receipts in one folder.
• Confirm the tax set-aside for the month was moved.
• Glance at net income by source, and note anything worth doing more or less of.

Fifteen minutes a month keeps tax season simple, because the totals you need are already in one place.

When to get professional help

If your side income grows, you have several income sources, or you're unsure what's deductible, a tax professional can save time and mistakes. The IRS also offers free help: its website has guides for the self-employed, and IRS Free File and Volunteer Income Tax Assistance (VITA) programs help eligible taxpayers file. Bringing clean records from your tracker makes any appointment faster.

This guide is general educational information, not financial, tax, legal, or insurance advice. Examples are illustrations, not predictions. See our disclaimer.