The lines this page follows
The 2025 Schedule SE says that if the combined profit line is more than zero, multiply it by 92.35 percent. That product is net earnings from self-employment before the optional methods, which this page does not offer. If that amount is less than $400, the form says to stop: you do not owe self-employment tax, except for a church-employee case this page also leaves out. Above that floor, the form multiplies the smaller of net earnings or the remaining Social Security wage base by 12.4 percent. It multiplies all of the net earnings by 2.9 percent. Those two products are the self-employment tax. Half of that tax is the deduction the form sends to Schedule 1.
Those percentages are what this calculator uses. The dollar figure printed on line 7 of the 2025 form is $176,100. That is the 2025 wage base, and it is the wrong cap for 2026. IRS Topic 751 says the base limit for earnings in 2026 is $184,500.00. The same figure is in the Social Security Administration's Federal Register notice of the 2026 contribution and benefit base. This page keeps 92.35 percent, 12.4 percent, 2.9 percent, the $400 stop, and the 50 percent deduction, and it uses $184,500 as the cap.
One hundred thousand dollars of profit
Start with $100,000 of net profit and no W-2 Social Security wages. Ninety-two point three five percent of $100,000 is $92,350.00. That is above $400, and it is under $184,500, so the whole amount is inside the Social Security base. Twelve point four percent of $92,350 is $11,451.40. Two point nine percent of $92,350 is $2,678.15. Added together, the self-employment tax is $14,129.55. Half of that, rounded to the cent, is $7,064.78. Those five figures are the check for this page. They are arithmetic on the form's rates, not a sample from a filled-in IRS form.
A tax form that rounds each line to the nearest dollar can land a dollar away from a cent-level product. This site's other money pages keep cents, and so does this one. If you are comparing the result with tax software, look at whether the software rounded line 4a, line 10, and line 11 before it added them. The rates should still be 92.35, 12.4, and 2.9. A difference of a dollar or two with the same rates is a rounding difference. A difference that uses 15.3 percent of the full $100,000 is a different method: that shortcut skips the 92.35 percent step the form requires.
The four-hundred-dollar stop
Profit of $400 times 92.35 percent is $369.40. The form stops when net earnings are under $400, so the tax on this page is $0.00. The stop is not a tax credit and it is not a standard deduction. It is a threshold on the self-employment tax itself. Income tax can still apply to the profit. The tax-bracket page starts from taxable income you type, after deductions, and it does not know that this profit exists.
The form's note about Conservation Reserve Program payments, and the church-employee lines that use 92.35 percent with a $100 floor, are not in this box. If either of those describes the return, Schedule SE's own instructions are the place to finish the form. This page will not invent an adjustment for them.
Wages that already used the wage base
Social Security tax stops once combined wages and self-employment earnings hit the base. Medicare tax does not. The form subtracts Social Security wages, unreported tips, and Form 8919 wages from the maximum, and it multiplies only the remaining room by 12.4 percent. If those wages are already $184,500.00, the room is zero. The same $100,000 of profit then has Social Security tax of $0.00 and Medicare tax of $2,678.15, which is still 2.9 percent of the $92,350. Type the W-2 Social Security wages, the boxes the form names, not the Medicare wages and not the gross pay. The paycheck page estimates the employee's 6.2 percent and 1.45 percent on wages. It is the other half of a W-2. It is not a substitute for Schedule SE, and this page is not a substitute for it.
What the total leaves out
The Additional Medicare Tax is 0.9 percent above the thresholds on Form 8959. The IRS questions-and-answers page for that tax is a separate worksheet from Schedule SE. This calculator does not add 0.9 percent, does not ask for filing status, and does not apply the $200,000, $250,000, or $125,000 thresholds. Leaving it out understates the Medicare-related tax for someone over those lines. That is a gap to close on the form, not a reason to guess the interaction here.
Net profit means the Schedule C or partnership figure the form starts from, after the ordinary business expenses that belong on those schedules. Typing gross receipts will overstate the tax. The optional farm and nonfarm methods, ministers who filed Form 4361, and the notary-public exception are also outside this page. Half of the self-employment tax reduces income subject to income tax. It does not reduce the self-employment tax itself. This page shows the deduction. It does not run it through the ordinary brackets.
Giuseppe Ilarda, the site owner, writes and checks the arithmetic. The disclaimer applies. The result is not a filled-in Schedule SE and it is not tax advice. If the form's instructions and this page disagree about a line this page claims to follow, the form controls, and the useful question is whether the profit and the Social Security wages you typed are the lines the form asked for.