Calculator Inputs
Use this estimate for part-time self-employment activity. Enter combined wage amounts if your filing status needs combined threshold testing.
Example Data Table
| Field | Example Value | Notes |
|---|---|---|
| Tax Year | 2025 | Uses 2025 Social Security wage base and mileage rate. |
| Gross Self-Employment Income | $30,000.00 | Total side income before business deductions. |
| Ordinary Expenses | $4,500.00 | Common costs like subscriptions, ads, and supplies. |
| Business Miles | 2,200 | Business-only miles used for deduction. |
| Home Office Method | Simplified | 180 square feet × $5 = $900.00. |
| W-2 Social Security Wages | $25,000.00 | Reduces the remaining Social Security cap. |
| W-2 Medicare Wages | $25,000.00 | Used against Additional Medicare threshold testing. |
| Result Focus | Total SE tax, deductible half, quarterly set-aside | Helpful for side-business tax planning. |
Formula Used
- Total deductions combine ordinary expenses, mileage deduction, home office deduction, and other business deductions.
- Net profit equals gross self-employment income minus total deductions.
- Taxable net earnings are 92.35% of net profit when profit is positive.
- Social Security tax applies at 12.4% only up to the remaining wage base after W-2 Social Security wages.
- Medicare tax applies at 2.9% to taxable net earnings when self-employment tax applies.
- Additional Medicare tax applies at 0.9% to self-employment income above the filing status threshold after reducing that threshold by Medicare wages already earned.
- Deductible half is an above-the-line deduction equal to half of total self-employment tax.
How to Use This Calculator
- Select the tax year and your filing status.
- Enter your part-time self-employment gross income.
- Add ordinary business expenses and any extra deductions.
- Enter business miles, then keep the default mileage rate or override it.
- Choose a home office method and complete the related field.
- Add W-2 wages already counted for Social Security and Medicare purposes.
- Press Calculate Tax to display the result section above the form.
- Review the summary, graph, deduction amount, and quarterly set-aside estimate.
- Use the CSV or PDF buttons to save the results.
Important Note
Frequently Asked Questions
1) What does this calculator estimate?
It estimates self-employment tax for part-time business income, including Social Security, Medicare, possible Additional Medicare tax, deductible half, and a quarterly set-aside target.
2) Why do W-2 wages matter here?
W-2 wages can already use part of the Social Security wage base. They can also reduce how much self-employment income remains before Additional Medicare tax starts.
3) Why are taxable net earnings lower than net profit?
Schedule SE generally applies the tax to 92.35% of net profit, not to the full profit figure. That adjustment is built into the calculator.
4) Does this include federal income tax too?
No. This page focuses on self-employment tax only. Federal income tax, state tax, credits, withholding, and estimated payment penalties are separate items.
5) Can I use actual vehicle expenses instead of mileage?
Yes, but this version uses a mileage method for simplicity. If you want actual vehicle expense support, replace mileage with your deductible vehicle total.
6) Why is my self-employment tax showing zero?
That usually happens when taxable net earnings are under $400 or when deductions reduce profit enough that self-employment tax no longer applies.
7) What is the deductible half used for?
Half of self-employment tax is commonly deductible as an adjustment to income. It lowers income tax calculation inputs, though it does not reduce self-employment tax itself.
8) Is this enough for filing my return?
It is helpful for planning, but filing still requires your full tax picture. Use your actual records and final tax forms before submitting a return.