1099 Deductions Calculator: What Each Write-Off Saves

Quick Answer: A 1099 deductions calculator multiplies your deductible business expenses by what each dollar saves: about 14.1 cents of self-employment tax (15.3% on 92.35% of the dollar) plus your marginal income tax rate on most of the rest. For most contractors that means a $1,000 write-off saves roughly $250 to $400 in federal tax, not $1,000. A spreadsheet with expenses by Schedule C line and one rate formula gives you the figure.

A write-off lowers the profit you pay tax on; it does not come back to you dollar for dollar. For an independent contractor filing Schedule C, each deductible dollar cuts both self-employment tax and income tax, so the saving is a percentage you can calculate. This guide builds that calculation in Excel or Google Sheets, line by line, so you can see what your actual expenses are worth.

Why isn't a $1,000 write-off worth $1,000?

Because the deduction comes off income, and tax is a percentage of income. If your expenses fall by $1,000, your net profit rises by $1,000, and the extra tax on that $1,000 is the most you were saving. The IRS tax brackets page explains that higher rates apply only to the layer of income in each bracket, so the rate that matters for a deduction is the one on your top layer, your marginal rate.

Self-employed people get a second layer of saving that employees do not: self-employment tax. The IRS self-employment tax page gives the rate as 15.3%, made up of 12.4% Social Security and 2.9% Medicare, and Schedule SE applies it to 92.35% of net profit (line 4a of the 2025 Schedule SE multiplies by 0.9235).

The formula behind the calculator

For each dollar of Schedule C expense:

1. Self-employment tax saved: 0.9235 × 0.153 = 0.1413, about 14.1 cents.
2. Income tax saved: your marginal rate × (1 − 0.1413 ÷ 2). The adjustment is there because half of self-employment tax is itself deductible when figuring adjusted gross income, so cutting SE tax slightly reduces that deduction.
3. Total per dollar: 0.1413 + marginal rate × 0.92935.

Add your state's income tax rate, if it has one, for a fuller picture. The rates themselves are on the IRS page for each tax year; the 2025 table was the current one there on 27 October 2026, with 2026 rates on a linked page.

Two limits change the result. Above the Social Security wage base (Schedule SE for 2025 shows $176,100 of combined wages and self-employment earnings), only the 2.9% Medicare part applies, so the self-employment piece drops to about 2.7 cents per dollar. And if you also have a W-2 job that already used up the wage base, the same applies. The qualified business income deduction, if you are eligible, also trims the income tax part a little; tax software handles it, and this calculator ignores it for simplicity.

Building it: three tabs

Inputs tab

The state rate is applied on the same base here as a simplification; states differ in how they treat self-employment tax.

Expenses tab, one row per Schedule C line. The Schedule C form numbers its expense lines 8 through 27b, with home office on line 30.

Results tab: =SUM(Expenses!C:C) for total deductions and =SUM(Expenses!D:D) for total tax saved. Dividing the second by the first should return your Inputs!B5 figure, which is a quick check that no row has a broken formula.

The home office and mileage rows

These two lines are calculated, not read from statements.

Home office. The IRS simplified option allows $5 per square foot of space used regularly and exclusively for business, up to 300 square feet. In the sheet: =MIN(SquareFeet,300)*5. A 150-square-foot office gives $750. The regular method can be larger but needs actual home costs and a business-use percentage; the home office deduction guide compares them.

Mileage. Under the standard mileage rate, the deduction is business miles times the IRS rate for the period driven. The IRS mileage rates page, read on 27 October 2026, shows 72.5 cents a mile for January to June 2026 and 76 cents for July to December 2026. Pull business miles from your log; building that log is covered in the mileage tracker spreadsheet. If you use the standard rate, leave gas and repairs off line 9.

A worked example

A freelance designer in the 22% bracket, in a state with a 5% income tax, below the wage base. Inputs!B5 = 0.1413 + 0.27 × 0.92935 = 0.392.

So $7,254 of write-offs is worth about $2,844 in combined federal and state tax for this person. Check any row: $1,200 × 0.392 = $470.40.

Where does the expense column come from?

From your business bank and card statements, categorized. Each charge that is a business expense goes to one Schedule C line; personal charges stay out. If your statements are PDFs, converting them to rows is the slow part; QuickBankConvert turns statement PDFs into CSV or Excel with dates, descriptions and signed amounts, and a free account covers a few statements a month. Add a column for the Schedule C line, then total with =SUMIFS(Amount,Line,8) and so on.

For which merchant types usually belong on which line, see bank statement deduction categories. Keep the receipts or invoices for larger items; a statement line shows the payment, not always what was bought.

What this calculator leaves out

• Your total tax bill. It shows the value of deductions, not what you owe. For the whole calculation with brackets and quarterly payments, use the self-employed tax calculator spreadsheet.
• Bracket edges. A large deduction can pull income from one bracket into the one below, so part of it saves at the lower rate.
• Depreciation choices. Equipment may be expensed at once or depreciated over years, which changes when the saving lands.
• Credits. Earned income credit and others can move in the opposite direction when income falls.
• Whether something is deductible at all. That is a question for the IRS rules or a tax professional, not the spreadsheet.

Related guides

• Bank statement deduction categories
• Self-employed tax calculator spreadsheet
• How much to save for taxes on 1099 income