Freelance projects, gig work, AI-powered side businesses, selling digital products, or consulting on the weekend: side income is one of the best ways to build savings, pay off debt, or fund a career change. It also comes with a tax surprise that catches many people off guard: no one withholds tax for you, and there's an extra tax on top of income tax.
This guide explains how US side income is taxed and how to stay ahead of it. It's in the career stage of our Money & Investing learning path, and it pairs with our AI side-income guides and real estate path.
Is side income taxable?
Yes. Income from freelancing, gig apps, consulting, selling things you make, online businesses, and similar work is taxable, whether or not you receive a tax form. If you're working for yourself with the aim of making a profit, the IRS generally treats you as self-employed, and you report the income and expenses on Schedule C.
A few distinctions:
- Selling your own used personal items for less than you paid isn't taxable profit, even if a payment app sends you a form. Keep records of what you paid.
- Hobby income is still taxable, but under current law, hobby expenses generally aren't deductible. If you're running it like a business, with the aim of profit, it's usually better treated as one.
- Rental income from property usually goes on Schedule E and generally isn't subject to self-employment tax. Our rental property guide covers the basics.
The 2026 changes to 1099 forms
Platforms and clients report payments to the IRS on 1099 forms:
- Form 1099-NEC: clients who pay you for services as a business generally send this. For payments made in 2026, the reporting threshold rises from $600 to $2,000, and it's set to adjust for inflation in later years.
- Form 1099-K: payment apps and online marketplaces send this. The threshold is over $20,000 and more than 200 transactions in a year.
These changes only affect who gets a form. They don't change what's taxable. If you earn $1,500 from a client and get no form, it's still income.
Self-employment tax: the part people miss
When you're an employee, Social Security and Medicare taxes are split: you pay half and your employer pays half. When you work for yourself, you pay both halves. That's self-employment (SE) tax:
- About 15.3% in total: 12.4% for Social Security (up to an annual wage base, shared with any wages from a job) and 2.9% for Medicare.
- It applies to 92.35% of your net self-employment earnings.
- It kicks in when net self-employment earnings are $400 or more for the year.
- You can deduct half of your SE tax when calculating income tax.
SE tax is on top of regular income tax, and it's the reason side income is taxed more heavily than many people expect.
A worked example: $20,000 of side profit
Say you have a full-time job and earn $20,000 of net profit (income minus business expenses) from freelance work. This simplified example ignores state tax and other details:
| Item | Calculation | Amount |
|---|---|---|
| Net self-employment profit | $20,000 | |
| SE tax | $20,000 × 92.35% × 15.3% | about $2,826 |
| Deduction for half of SE tax | about −$1,413 | |
| Qualified business income (QBI) deduction | Up to 20% of qualified business income, subject to limits | about −$3,717 |
| Added taxable income | about $14,870 | |
| Federal income tax at a 22% bracket | about $3,271 | |
| Total federal tax on the side income | about $6,097 (about 30% of profit) | |
| Same example at a 12% bracket | about $4,610 (about 23%) |
That's why a common rule of thumb is to set aside 25% to 30% of side profit for taxes, more if you're in a higher bracket or a high-tax state. Paying about $6,100 over the year is roughly $1,525 per quarter.
Simplified illustration only. Your actual tax depends on your total income, filing status, deductions, credits, and state.
Quarterly estimated taxes
Because nobody withholds tax from side income, the IRS expects you to pay during the year. If you expect to owe $1,000 or more when you file, you generally need to make estimated tax payments.
Usual due dates (moved to the next business day if they fall on a weekend or holiday):
| Payment | Covers income from | Due |
|---|---|---|
| 1 | January 1 to March 31 | April 15 |
| 2 | April 1 to May 31 | June 15 |
| 3 | June 1 to August 31 | September 15 |
| 4 | September 1 to December 31 | January 15 of the next year |
You can pay through IRS Direct Pay, your IRS online account, or EFTPS. Form 1040-ES includes a worksheet for estimating the amount.
Avoiding the underpayment penalty
You generally avoid a penalty if your withholding and estimated payments cover at least:
- 90% of this year's tax, or
- 100% of last year's tax (110% if last year's adjusted gross income was over $150,000).
Paying based on last year's tax is the simplest safe harbor when your side income is growing.
The easier option if you have a day job
Instead of quarterly payments, you can increase the tax withheld from your paycheck by updating your Form W-4 with your employer. Withholding is treated as paid evenly through the year, even if you increase it late in the year. The IRS Tax Withholding Estimator helps you work out the amount.
Deductions: what's legitimate
You pay tax on profit, not revenue, so legitimate business expenses reduce your tax. Expenses generally need to be ordinary and necessary for your business. Common examples:
| Expense | Notes |
|---|---|
| Software and subscriptions | Tools used for the business, including AI tools, design software, and hosting |
| Equipment | Computers, cameras, and gear used for business; mixed personal use must be split |
| Home office | Only for space used regularly and exclusively for business. The simplified method is $5 per square foot, up to 300 square feet |
| Vehicle use for business | Standard mileage rate or actual expenses, with a mileage log. Commuting doesn't count |
| Internet and phone | The business-use percentage |
| Training and education | Courses that maintain or improve skills for your current business |
| Advertising and marketing | Websites, ads, business cards |
| Professional services | Tax preparation for the business, legal fees |
| Health insurance premiums | Many self-employed people can deduct premiums, subject to rules |
| Retirement contributions | See below |
Red flags to avoid: deducting personal expenses, claiming 100% business use of things you use personally, or deducting a home office you also use as a guest room. Deductions you can't support with records can be disallowed, with interest and penalties.
Retirement accounts for the self-employed
Self-employed people can save for retirement and lower their taxes at the same time:
- SEP IRA: simple to open; employer-style contributions up to a percentage of net self-employment earnings.
- Solo 401(k): for self-employed people with no employees other than a spouse; allows both "employee" and "employer" contributions, often letting you save more at lower incomes than a SEP. Many offer a Roth option.
If you also have a 401(k) at your day job, your employee contribution limit is shared across plans. Our retirement accounts guide covers the 2026 limits and the traditional vs Roth choice.
Set up a simple system
- Open a separate bank account for business income and expenses. It makes bookkeeping and deductions far easier.
- Move a fixed percentage of every payment, such as 25% to 30%, into a separate tax savings account the day it arrives. Treat it as untouchable, like an emergency fund.
- Track income and expenses monthly in a spreadsheet or accounting tool. Our data analysis guide covers building a simple tracker.
- Keep receipts and records. The IRS generally asks you to keep records supporting your return for at least three years, and longer in some situations.
- Calendar the four estimated tax dates.
- Review each quarter: profit so far, tax set aside, and payments made.
- Check state rules. Most states tax income too, and some have their own estimated payment requirements.
Special cases
- Gig apps and delivery work: you're usually an independent contractor. Track mileage carefully; it's often the largest deduction.
- Selling online: know the difference between a business (profit-seeking, regular sales) and selling occasional personal items.
- AI-powered businesses: subscriptions to AI tools, API costs, and hosting used for the business are generally deductible business expenses. Our making money with AI connectors guide covers the business side.
- Real estate: rental income generally goes on Schedule E, not Schedule C. Flipping properties or real estate services can be self-employment income. See our real estate path.
- Payment scams: fake "IRS" calls and texts demanding immediate payment by gift card or crypto are scams. The IRS doesn't demand payment that way. Our phishing guide covers the tactics.
Frequently asked questions
How much should I set aside for taxes on side income?
A common starting point is 25% to 30% of profit, covering self-employment tax and federal income tax. Set aside more if you're in a higher bracket or a high-tax state.
Do I have to pay taxes if I didn't get a 1099?
Yes. All income is taxable whether or not a form is issued. 1099 thresholds only determine who receives a form.
Do I have to pay quarterly taxes if I have a full-time job?
Not necessarily. If your withholding covers enough of your total tax to meet a safe harbor, you can avoid penalties. Many people with day jobs simply increase their W-4 withholding instead of making quarterly payments.
What is the self-employment tax rate?
About 15.3% (12.4% Social Security, up to an annual wage base, plus 2.9% Medicare), applied to 92.35% of net self-employment earnings once they reach $400. Half of it is deductible for income tax.
Can I deduct my home office?
Only if you use the space regularly and exclusively for your business. The simplified method allows $5 per square foot, up to 300 square feet.
Check your understanding
Answer each question from memory before opening it. Recalling, not rereading, is what makes learning stick (here's why).
1 What is self-employment tax, and roughly what rate is it?
Social Security and Medicare tax for people who work for themselves, about 15.3% on most net self-employment earnings, because you pay both the employee and employer shares.
2 Is side income taxable if you don't receive a 1099 form?
Yes. All income is taxable whether or not a form is issued. The 2026 change to a $2,000 1099-NEC threshold only changes who gets a form.
3 What are the four usual due dates for quarterly estimated taxes?
April 15, June 15, September 15, and January 15 of the following year (moved to the next business day if one falls on a weekend or holiday).
4 What's a safe harbor for avoiding an underpayment penalty?
Paying at least 90% of this year's tax, or 100% of last year's tax (110% if last year's adjusted gross income was over $150,000), through withholding and estimated payments.
5 If you have a day job, what's a simple alternative to quarterly payments?
Increase the tax withheld from your paycheck by updating your Form W-4, since withholding is treated as paid evenly through the year.
Where to go next
You've finished the career stage of the Money & Investing path. Next:
- Retirement accounts explained: including SEP IRAs and Solo 401(k)s.
- Creative ways to make money with AI: realistic side-income ideas.
- How to pay off debt and build your credit score: a strong place to send side income.
Sources
- IRS: Self-employed individuals tax center: SE tax, Schedule C, and estimated taxes.
- IRS: Gig economy tax center: rules for gig and app-based work.
- IRS: Estimated taxes: due dates, Form 1040-ES, and safe harbors.
- IRS: Tax Withholding Estimator: adjust paycheck withholding for side income.
- IRS: Home office deduction: eligibility and the simplified method.
- IRS: Retirement plans for self-employed people: SEP IRAs and Solo 401(k)s.