Quarterly Tax Set-Aside Calculator
Estimate the full tax on your business income — self-employment tax, federal income tax, and optional state tax — so you know exactly how much to set aside each month and pay each quarter.
When you're self-employed, no one withholds taxes for you — it's on you to set the money aside and pay the IRS four times a year. Underestimate, and you're hit with a surprise bill plus underpayment penalties. This calculator estimates the full tax on your business income — self-employment tax, the federal income tax it adds on top of your other income, and optional state tax — so you know exactly how much to keep aside.
Enter your numbers below to get a recommended monthly set-aside and your four quarterly estimated payments with their due dates.
Quarterly Tax Set-Aside Calculator
Updates live as you change any number.
Net profit after business expenses (Schedule C bottom line)
Sets your standard deduction and tax brackets
W-2 wages or a spouse's income (default $0)
Applied to your business income (default 0% — no state tax)
Set Aside Each Month
$51,398 total estimated tax on your business income · 34.3% effective rate
How Your Estimate Breaks Down
Your Four Quarterly Payments
Q1
$12,850
Due April 15, 2025
Q2
$12,850
Due June 15, 2025
Q3
$12,850
Due September 15, 2025
Q4
$12,850
Due January 15, 2026
Total = self-employment tax + the federal income tax your business income adds on top of your other income + optional state tax. The monthly figure is that total ÷ 12; each quarterly payment is the total ÷ 4. Filing status Single with a $15,000 standard deduction (2025).
How the Math Works
Self-employment tax:
SE income = Business income × 0.9235
Social Security = min(SE income, $176,100) × 12.4%
Medicare = SE income × 2.9%
Federal income tax (incremental):
AGI = Business income + Other income − ½ SE tax
Taxable = max(0, AGI − Standard deduction)
Federal = tax(taxable WITH business) − tax(taxable WITHOUT business)
Total:
Total = SE tax + Federal + (Business income × State rate%)
Monthly = Total ÷ 12 | Quarterly = Total ÷ 4
Two things make self-employment taxes higher than people expect. First, the self-employment tax (15.3% on most of your profit) is on top of income tax. Second, business profit stacks on top of your other income, so it's taxed at your highest marginal rates — which is why this tool isolates the incremental federal tax rather than applying an average rate to the whole profit.
2025 Figures Used
Self-Employment Tax
Applied to 92.35% of net profit: 12.4% Social Security up to the $176,100 wage base, plus 2.9% Medicare on all of it.
Standard Deduction
Single $15,000 · Married Filing Jointly $30,000 · Head of Household $22,500.
Federal Income Tax Brackets
The 2025 IRS marginal brackets (10% to 37%) for your filing status. Income tax is progressive — each portion of income is taxed at its own bracket rate, not a single flat rate.
This Is an Estimate — Not Tax Advice
- This tool gives a planning estimate only and is not tax, legal, or accounting advice.
- It doesn't account for credits, itemized deductions, the QBI deduction, retirement contributions, or income that varies during the year.
- State tax is a simple flat rate on business income and ignores state-specific deductions, brackets, and local taxes.
- Quarterly due dates shift to the next business day on weekends and holidays. Always confirm your exact liability with a CPA before paying or filing.
Want Exact Quarterly Numbers?
Mana handles quarterly estimates for our clients — calculated from your real books, adjusted as your income changes, and filed on time so you never get a surprise bill or a penalty.
Frequently Asked Questions
Why do I owe self-employment tax on top of income tax?
When you're self-employed you pay both the employee and employer halves of Social Security and Medicare — that's the 15.3% self-employment tax (applied to 92.35% of your net profit). A W-2 employee splits this with their employer; a business owner covers both sides. It's separate from, and on top of, federal income tax.
Why does this calculate the 'incremental' federal income tax?
Your business profit stacks on top of any other household income, so it's taxed at your marginal rates. To isolate what the business actually owes, the calculator figures your federal income tax with the business income and again without it, then takes the difference. That's a more accurate set-aside than applying a flat rate to the profit.
When are quarterly estimated taxes due?
For the 2025 tax year the four federal deadlines are April 15, 2025, June 15, 2025, September 15, 2025, and January 15, 2026. If a date falls on a weekend or holiday it shifts to the next business day. Missing them can trigger underpayment penalties even if you pay in full by the April filing deadline.
Is setting aside this amount each month enough?
Setting aside the recommended monthly figure in a separate account is a strong habit and usually covers the bill. But your actual liability depends on deductions, credits, other income, and how your year plays out. Treat this as a planning estimate and reconcile with a CPA before you file — especially if your income changes mid-year.