1. Start with your net profit
Business income minus business expenses: the bottom line of Schedule C. A married consultant expects $85,000 of profit in 2026. Her spouse earns $40,000 in wages.
2. Calculate self-employment tax
Multiply profit by 92.35%, then by 15.3% (12.4% Social Security on the first $184,500 of earnings, plus 2.9% Medicare). $85,000 × 0.9235 = $78,498; × 0.153 = $12,010.
3. Deduct half of it
Half of self-employment tax ($6,005) is deducted from income before income tax is figured.
4. Find taxable income
Total income minus that deduction minus the 2026 standard deduction ($32,200 married filing jointly; $16,100 single): $40,000 + $85,000 − $6,005 − $32,200 = $86,795.
5. Apply the 2026 brackets, and isolate the business
For married filing jointly, 10% on the first $24,800 and 12% up to $100,800. Tax on $86,795 is about $9,919. Without the business, taxable income would be $7,800 and tax $780, so the business adds about $9,139 of federal income tax. (The spouse’s paycheck withholding already covers part of the $780.)
6. Total and divide by four
$12,010 + $9,139 = about $21,150, or 25% of profit, before any state income tax. An even quarterly payment is about $5,287.
When to pay
For the 2026 tax year: April 15, June 15 and September 15, 2026, and January 15, 2027. You can generally avoid an underpayment penalty by paying at least 90% of this year’s tax or 100% of last year’s (110% if last year’s adjusted gross income was over $150,000). Payments are made through IRS Direct Pay or your IRS online account.
In a spreadsheet
B1: Profit (85000)
B2: SE tax: =B1*0.9235*0.153 (exact up to $184,500 of earnings)
B3: Half deduction: =B2/2
B4: Then run taxable income through your bracket, with and without the business
An estimate, not tax advice. This leaves out the qualified business income deduction, credits and itemized deductions, so it usually runs a little high. A tax professional can give you an exact figure.
Published by Groundwork Business Advisory. Updated October 19, 2026.