What Is a Tax Write-Off? How Deductions Cut Your Bill

A tax write-off, also called a tax deduction, is an expense the IRS lets you subtract from your income before your tax is calculated, so you are taxed on a smaller amount. It is not a dollar-for-dollar discount on your bill: a write-off lowers your taxable income, and its real value equals the deduction multiplied by your marginal tax rate. A $1,000 write-off saves someone in the 22 percent bracket about $220 in income tax, not $1,000.

Write-off vs tax credit: the difference that trips people up

People use "write-off" loosely, but in tax terms it means a deduction, and a deduction is not the same as a credit. The distinction changes how much money you actually save, so it is worth getting straight before you count on either one.

A credit is worth more per dollar because it cuts the tax itself. A deduction only cuts the income the tax is figured on. Both help, but when someone tells you an expense is "a write-off, so it's basically free," they are wrong. You still pay for it; you just pay a little less tax because of it.

The three kinds of write-offs

Deductions come in three flavors, and they stack in a specific order on your Form 1040.

• Above-the-line adjustments. These come off your gross income to reach your adjusted gross income (AGI), and you get them whether or not you itemize. Examples: the deductible half of self-employment tax, self-employed health insurance, HSA contributions, IRA contributions, and student loan interest.
• The standard deduction. A flat amount you subtract with no receipts required. For tax year 2025 it is $15,750 for single filers, $31,500 for married filing jointly, and $23,625 for head of household. Most filers take this.
• Itemized deductions. Listed on Schedule A and taken instead of the standard deduction, but only if they add up to more. Mortgage interest, state and local taxes, charitable gifts, and large medical bills are the common ones.

You pick the standard deduction or itemizing, whichever is larger, but above-the-line adjustments and business write-offs are separate and come off regardless.

Business write-offs are the most valuable kind

If you are self-employed, a freelancer, or run a small business, your best write-offs live on Schedule C, not Schedule A. A business expense reduces your net profit, and your net profit is what both income tax and the 15.3 percent self-employment tax are calculated on. So a legitimate Schedule C write-off cuts two taxes at once, which is why it saves more than an itemized deduction of the same size.

The rule for what counts is set by the tax code: an expense has to be ordinary and necessary for your trade or business (IRC Section 162). "Ordinary" means common and accepted in your line of work. "Necessary" means helpful and appropriate. It does not have to be indispensable. Common Schedule C write-offs include:

The catch is records. You can only claim what you can support, so keep receipts, a mileage log, and clean books through the year. If your bookkeeping lives in QuickBooks, you can turn each bank statement into a QuickBooks file instead of typing transactions in by hand, which makes deduction season far less painful. Our full 1099 deductions list walks through the write-offs contractors miss most.

The QBI deduction: a write-off you do not spend money on

Most write-offs cost you something first. The Qualified Business Income (QBI) deduction is different. It lets eligible self-employed people and pass-through business owners deduct up to 20 percent of their qualified business income, with no cash outlay. It is a deduction, not a credit, so it lowers taxable income. The 2025 tax law made it permanent and added a minimum $400 deduction for taxpayers with at least $1,000 of active qualified business income. If you earn $60,000 of net profit from freelancing, the QBI deduction can knock roughly $12,000 off the income you are taxed on.

How much a write-off actually saves you

Because a write-off works through your marginal rate, the same expense saves different people different amounts. Here is a $1,000 deductible business expense for a self-employed filer, where it cuts both income tax and self-employment tax:

The self-employment tax piece is why business write-offs beat personal ones. A W-2 employee who itemizes a $1,000 deduction saves only the income-tax portion. A Schedule C filer saves that plus roughly 14 percent in self-employment tax, because the deduction shrinks the profit both taxes are based on.

Frequently asked questions

What is a tax write-off?

A tax write-off is another name for a tax deduction: an expense the IRS lets you subtract from your income so you are taxed on less. It reduces your taxable income, not your tax bill directly, so its value is the deduction times your marginal tax rate. For a business, ordinary and necessary expenses are written off on Schedule C.

Does a write-off mean the expense is free?

No. A write-off only lowers your taxable income, so you recover a fraction of the cost equal to your tax rate. A $1,000 expense for someone in the 22 percent bracket saves about $220 in income tax. You still paid the other $780. Buying something you do not need just to "write it off" always loses money.

What can I write off if I am self-employed?

You can write off ordinary and necessary business expenses on Schedule C: home office, business mileage at 70 cents per mile for 2025, phone and internet, software, supplies, advertising, contract labor, and business insurance. You also deduct half of your self-employment tax and may qualify for the 20 percent QBI deduction. Keep receipts and records for everything you claim.

Is a write-off the same as a tax credit?

No. A write-off (deduction) reduces the income your tax is calculated on, while a credit reduces the tax you owe dollar for dollar. A $1,000 credit is worth the full $1,000; a $1,000 deduction is worth only $1,000 times your tax rate. Credits are more valuable per dollar, but deductions are far more common.

Do I need receipts for my write-offs?

Yes. You can only deduct expenses you can prove, so keep receipts, invoices, bank and card statements, and a mileage log. The IRS can ask you to substantiate any deduction, and without records a write-off can be disallowed on audit. Clean bookkeeping through the year is the difference between claiming a deduction and losing it.

TaxFile is self-prepared tax software and does not provide personalized tax advice. Deduction rules have limits and exceptions; for a complex situation, consult a CPA or tax professional.