Tax Deduction Calculator

By the · Last updated September 16, 2026

✅ Current for tax year 2026

Deductions don’t just lower an abstract “taxable income” number — they lower a real tax bill, in real dollars. This calculator shows the actual before-and-after difference so you can see what a home office, some mileage, or a retirement contribution is genuinely worth to you.

How this calculator works

Enter your net income before deductions, then fill in whatever categories apply to you. The calculator runs your income through the same 2026 self-employment and federal income tax rules twice — once at your full income, once after subtracting your deductions — and shows you the real dollar gap between the two. That gap is what your deductions are actually worth this year, not a rough percentage guess.

Why this beats a flat percentage estimate

A lot of quick “your deduction is worth X%” advice glosses over how self-employment tax and income tax interact — the same dollar of deduction is worth a different amount depending on your income level and filing status. Running the numbers before and after gets you a real answer instead of a rule of thumb.

What’s not included

This estimate covers federal self-employment and income tax only — not state taxes, the Qualified Business Income deduction, or tax credits, all of which could change your real number further. See the full deductions list for what else might apply to you and current dollar limits for things like retirement contributions.

A quick example

Say your net income before deductions is $70,000. Without factoring in any deductions, your combined self-employment and federal income tax might land around $16,500. Add a $6,000 home office and mileage deduction, a $4,000 SEP-IRA contribution, and $3,600 in self-employed health insurance premiums — $13,600 in total deductions — and that same calculation might drop to roughly $13,200. The $3,300 gap between those two numbers is what your deductions were actually worth this year, in real dollars, not a rough percentage estimate.

Deductions that reduce tax differently

Not every deduction works the same way. Business expenses (mileage, software, supplies) reduce your Schedule C net profit directly, which lowers both self-employment tax and income tax. Retirement contributions and self-employed health insurance reduce your AGI, but only after self-employment tax has already been calculated on your full net profit — so they lower your income tax but not your self-employment tax. A $5,000 business expense and a $5,000 SEP-IRA contribution both save you money, but not the identical amount, because they hit different points in the calculation. This calculator runs the actual math rather than treating every dollar of deduction as interchangeable.

When to run this before filing

Running this calculator isn’t just useful at tax time — checking it mid-year, after a major purchase or a new retirement contribution, helps you see in real time whether adjusting your quarterly payments makes sense. A large deduction that lands in Q3 can lower what you owe for the rest of the year, and catching that early avoids overpaying a quarterly estimate based on outdated numbers.

Timing deductions across tax years

Some deductible purchases give you a choice about which year to claim them, depending on when you actually pay for them — buying a laptop on December 28th versus January 3rd puts the exact same expense in two different tax years. If your income is unusually high this year and you expect it to be lower next year, accelerating a planned purchase into the current year captures the deduction when it’s worth more, since deductions save you your marginal rate, and a higher-income year generally means a higher marginal rate. This kind of timing decision only makes sense for purchases you were already planning to make — buying something you don’t need purely for a tax deduction almost never makes financial sense, since you’re still spending more than you save.

Bunching deductions in alternating years

For certain deductions with dollar thresholds or phase-outs, concentrating discretionary business spending into alternating years — a bigger equipment purchase this year, none next year — can sometimes produce a better combined result than spreading identical spending evenly across both years. This strategy matters more for itemized personal deductions than most standard business expenses, which are simply deductible whenever paid, but it’s worth knowing as a general concept if you’re planning significant business investments and have some flexibility in timing them.

Keep reading

• Mileage deduction calculator — get an exact dollar figure for your business driving first.
• 1099 & quarterly tax calculator — see your full tax picture and quarterly payment.