The short version
Social Security tax only applies up to a yearly limit — the wage base, $184,500 in 2026. Your W-2 wages count toward that limit first. Whatever room is left over is all the self-employment income that can be hit by the 12.4% Social Security part. Medicare (2.9%) has no limit, so it applies to all of your SE earnings either way.
Example: $150,000 salary and $60,000 side profit
The calculator is set to $150,000 of W-2 wages (box 3 of your W-2) and $60,000 of net profit from your side business in 2026, filing single.
- Net SE earnings: $60,000 × 92.35% = $55,410.
- Room left under the wage base: $184,500 − $150,000 = $34,500.
- Social Security: 12.4% of $34,500 (not of $55,410) = $4,278.00.
- Medicare: 2.9% of all $55,410 = $1,606.89. SE tax = $5,884.89.
- Additional Medicare: the 0.9% threshold for single filers is $200,000, reduced by your $150,000 of wages, leaving $50,000. Your SE earnings are $5,410 above that, so you owe $48.69 on Form 8959.
- Total: $5,933.58. You can deduct half of the SE tax, $2,942.45.
Without the day job, the same $60,000 profit would cost $8,477.73. The wage base saves you $2,592.84 here — money your employer’s payroll already covered.
How different salaries change it
Same $60,000 side profit in 2026, single:
| W-2 wages | Social Security on side income | Additional Medicare | Total SE-related tax |
|---|---|---|---|
| $0 | $6,870.84 | $0.00 | $8,477.73 |
| $50,000 | $6,870.84 | $0.00 | $8,477.73 |
| $100,000 | $6,870.84 | $0.00 | $8,477.73 |
| $150,000 | $4,278.00 | $48.69 | $5,933.58 |
| $184,500 | $0.00 | $359.19 | $1,966.08 |
| $200,000 | $0.00 | $498.69 | $2,105.58 |
Once your wages reach $184,500, the Social Security part on your side income drops to zero. You still pay 2.9% Medicare, plus the 0.9% Additional Medicare once wages and SE earnings together pass $200,000.
Married filing jointly?
Choose “Married filing jointly” and enter your spouse’s wages. The wage base is per person, so only your own wages reduce your Social Security part. Your spouse’s wages only matter for the $250,000 Additional Medicare threshold.
A handy tip for paying it
Instead of making quarterly estimated payments, you can ask your employer to withhold a bit more federal income tax by updating your Form W-4 (step 4(c), “extra withholding”). Withholding counts as if it were paid evenly through the year, so it can cover the tax on your side business too — even if you only change it late in the year. Many people with a day job find this the easiest way.
If you have two or more W-2 jobs, add their Social Security wages together. If together they exceed $184,500, you can claim back excess employee Social Security tax withheld on your return.
FAQ
Does my W-2 job reduce my self-employment tax?
Yes, the Social Security part. With $150,000 of wages in 2026, only $34,500 of SE earnings is left under the $184,500 wage base, so the 12.4% part is $4,278.00 instead of $6,870.84.
Do I still pay Medicare on my side income?
Yes. The 2.9% Medicare part has no limit: on $60,000 of profit it is $1,606.89. Above $200,000 of combined wages and SE earnings (single), another 0.9% applies — $48.69 in this example.
What is my total if I earn $150,000 in wages and $60,000 on the side?
$5,933.58 of SE-related tax for 2026: $5,884.89 SE tax plus $48.69 Additional Medicare. Half of the SE tax, $2,942.45, is deductible.
Sources (checked 5 November 2026): SSA “2027 Social Security Changes” fact sheet (ssa.gov/cola/factsheets/2027.html — maximum taxable earnings $184,500 for 2026 and $192,300 for 2027; self-employed rate 15.3%); IRS Taxpayer Advocate Service “Important tax dates 2026”; IRS estimated tax FAQ (weekend/holiday rule, updated 16 Oct 2026); IRC §§ 1401, 1402 and 164(f); Form 8959 and Schedule SE instructions.