Two jobs and federal withholding

This calculator always treats the wage you typed as the only wage for the year. That is the same assumption a W-4 uses when the multiple-jobs checkbox is off. If you have two jobs, or you are married filing jointly and both spouses work, stacking two “single job” take-home numbers will usually overstate combined take-home. Each job withholds as if its own standard deduction and 10% bracket were still fully available. They are not. There is one standard deduction per return.

What goes wrong in numbers

Suppose job A pays $45,000 and job B pays $40,000, both single in this model, no dependents. Run $45,000: the site subtracts the full $16,100 single standard deduction and taxes the rest through the bottom brackets. Run $40,000: it does that again. In the real world you have one $16,100 deduction and one stack of brackets on $85,000 of wages (before other adjustments). A large slice of the second job is taxed in a higher bracket than either isolated run showed. The IRS built W-4 Step 2 and the two-earners worksheet for that gap. This site does not implement Step 2.

What you can do with this page anyway

Enter the combined annual wage as one salary if both jobs are W-2 and you want a rough combined federal + FICA picture. That still misses different pay frequencies, two Social Security wage-base clocks, and extra withholding already set on one job. It is closer than adding two isolated results. Then compare federal lines on the two stubs, not nets, because state tax and benefits still sit outside this model. Details: federal withholding and FICA vs income tax.

FICA is the exception people mix up

Social Security and Medicare are not shared the way the standard deduction is. Each employer withholds FICA on the wages it pays, up to the Social Security wage base at that employer. Two jobs can withhold Social Security on more than the annual wage base combined. You often get the excess back at filing. This calculator will not show that refund. Additional Medicare Tax (0.9% over $200,000 at one employer, with different thresholds on a joint return) is also a filing-time true-up. Do not use a stacked pair of estimates to decide whether you will owe that extra 0.9%.

Married, both working

Pick married filing jointly only if that is the status you will file. Then either enter combined wages as one salary for a rough federal picture, or use the IRS estimator which is built for two jobs. Entering married jointly on a $45,000 job while the spouse also works $45,000 is how people under-withhold: this site thinks the whole joint standard deduction belongs to that one job.

Related: how W-4 maps to this calculator. Not tax advice.