A tax write-off is a business cost you subtract from your income before your tax is calculated. If you earned $60,000 and spent $10,000 running the business, you are taxed on $50,000 rather than $60,000 — the write-off reduces the income being taxed, not the tax bill itself.
That distinction is the whole subject, and it is where almost everyone starts out wrong. This guide explains what a write-off is worth in real money, what qualifies, what does not, and what you have to keep to claim one. It assumes you know nothing about tax vocabulary. If you also need to know when your return is actually due, that is a separate question with its own dates.
What a tax write-off actually is
"Write-off", "deduction" and "business expense" all mean the same thing in ordinary conversation. Formally it is a deduction: an amount subtracted from your gross income to arrive at the taxable income your tax is calculated on.
A $100 write-off does not save you $100. It saves you $100 multiplied by your marginal tax rate — the rate that applies to your next dollar of income. Work it through:
- You are self-employed and your next dollar of income is taxed at 22%.
- You buy a $1,000 laptop that is genuinely for the business.
- Your taxable income drops by $1,000.
- Your tax bill drops by roughly $220 — not $1,000. You are still $780 out of pocket.
For a self-employed person the real saving is usually somewhat larger than that, because a business deduction on Schedule C reduces your net profit, and self-employment tax is calculated on that profit as well. So the same $1,000 laptop reduces two taxes rather than one. It still does not make the laptop free.
This is why "just write it off" is never a reason to buy something. A write-off makes a cost you were going to incur anyway cheaper. It never makes an unnecessary purchase profitable. The only situation where spending $1,000 to save $220 is a good trade is when you wanted the thing for $1,000 in the first place. Estimates — confirm with your tax professional.
Write-off vs tax credit
People use these interchangeably and they are not the same. A deduction reduces the income you are taxed on. A credit reduces the tax you owe, dollar for dollar.
| Deduction (write-off) | Tax credit | |
|---|---|---|
| What it reduces | Your taxable income | The tax you owe |
| What $1,000 of it is worth | $1,000 × your marginal rate | $1,000 |
| At a 22% rate | About $220 | $1,000 |
| Typical examples | Business supplies, software, mileage, home office | Child tax credit, certain energy credits |
Per dollar, a credit is worth far more. You do not get to choose between them — an expense is one or the other by law — but knowing the difference stops you overestimating what a deduction is doing for you.
What counts as a business write-off
The US standard is that an expense must be ordinary and necessary for your trade or business. "Ordinary" means common and accepted in your line of work. "Necessary" means helpful and appropriate — not that you could not possibly have operated without it. Both words are broader than they sound, which is why the same purchase can be deductible for one person and not another. A camera is ordinary and necessary for a photographer and not for a plumber.
Common examples for a self-employed person:
- Software subscriptions and web hosting used for the business
- Supplies, equipment and tools
- Business-related travel
- Professional fees — your accountant, your lawyer
- Advertising and marketing
- Business insurance
- Business mileage in your own vehicle
- A home office, when the space is used regularly and exclusively for the business
Mixed-use items are deducted by business-use percentage. If a phone plan is 60% business and 40% personal, you deduct 60% of it. The percentage has to be defensible — it should reflect actual use, and you should be able to explain how you arrived at it. The same logic applies to a car, a laptop, or an internet connection; our post on deducting a home internet bill works through one of these in detail.
Some categories have their own rules layered on top. Business mileage can be claimed using a standard per-mile rate that the IRS sets and revises — see the current IRS mileage rate for the figures and the mid-year change. Business meals are generally limited to 50% of the cost under IRS Publication 463, with narrow exceptions. Estimates — confirm with your tax professional.
What people wrongly think they can write off
These come up constantly, and getting them wrong is what turns an audit into an expensive one.
- Commuting. Driving between home and your regular place of work is personal, not business, no matter how far it is. Driving from your workplace to a client and back is business. This trips up more people than any other item on the list.
- Everyday clothing. A suit you bought for client meetings is not deductible, because it is suitable for ordinary wear. Genuinely unsuitable-for-daily-wear items — a branded uniform, protective gear — generally are.
- The full cost of business meals. The general rule limits you to 50%, and the meal has to have a business purpose with you present. A meal alone, with no business being conducted, is not a business meal.
- Your entire phone bill. Unless the line is exclusively for business, you deduct the business-use percentage, not the whole thing.
- A home office you also use as a spare room. The regular-and-exclusive-use test means the space has to be used for the business and not for anything else. A desk in the corner of a bedroom that doubles as a guest room does not qualify.
- Personal costs with a business justification attached after the fact. A gym membership is the classic case — the business rationale people construct for it almost never survives contact with the actual rule. Our post on writing off a gym membership explains where the narrow exception sits.
The pattern behind all of these: the test is what the expense genuinely is, not what you call it. Renaming a personal cost does not convert it.
What you need to keep
A deduction you cannot substantiate is a deduction you may lose. For each expense you want five things:
- The date
- The amount
- The merchant
- What was purchased
- The business purpose — why this was a business cost
A receipt normally carries the first four. The fifth is the one people skip, and it is the one that matters most for anything that could plausibly be personal. "Lunch, $48" is weak. "Lunch, $48, with Dana Okafor of Harlow Studio, discussing the Q4 contract" is not.
Digital copies are fine. The IRS accepts digital records under Rev. Proc. 97-22 provided they are legible and accurately reproduce the original, and the CRA accepts electronic records under its own record-keeping guidelines. Since thermal receipts fade within months, a photo taken the day you get one is more durable than the paper itself.
If you have already lost the receipt, that is a narrower question with a real answer — see claiming deductions without receipts, which covers what courts have allowed and, importantly, the categories where estimates are not accepted at all.
The practical problem for most self-employed people is not knowing the rules — it is that receipts are scattered across an inbox, a wallet and a camera roll, and reconstructing a year of them in April is how deductions get missed. ExpenseBot scans your Gmail for receipts that already arrived by email, extracts the date, merchant, amount and line items, and writes each one into a Google Sheet in your own Drive, with photos of paper receipts landing in the same place. The point is that the record exists in March rather than being rebuilt in April. It is a way of keeping the evidence, not tax advice — and it does not file for you.
Once you know what a write-off is worth, the two things that follow are keeping the records and filing on time. For the second, our guide to tax filing deadlines has the dates, including the quarterly estimated-payment ones that catch newly self-employed people in their first year. Estimates — confirm with your tax professional.
Frequently Asked Questions
What is a tax write-off in simple terms?
A business cost you subtract from your income before your tax is calculated. If you earned $60,000 and had $10,000 of legitimate business expenses, you are taxed on $50,000 instead of $60,000. "Write-off", "deduction" and "business expense" all describe the same thing in ordinary conversation. Estimates — confirm with your tax professional.
How much money does a write-off actually save me?
The amount of the expense multiplied by your marginal tax rate — not the full amount. A $1,000 write-off for someone whose next dollar is taxed at 22% saves roughly $220, not $1,000. This is the single most common misunderstanding about write-offs, and it is why "just write it off" is never a reason to buy something you did not otherwise need. Estimates — confirm with your tax professional.
Is a write-off the same as a tax credit?
No, and the difference matters. A deduction reduces the income you are taxed on, so it is worth your marginal rate. A credit reduces the tax you owe, dollar for dollar. A $1,000 credit cuts your bill by $1,000; a $1,000 deduction cuts it by your rate times $1,000. Per dollar, a credit is worth substantially more.
Can I write off expenses without a receipt?
Sometimes, but it is a fallback rather than a plan. Courts have allowed reasonable estimates for some expenses under what is known as the Cohan rule, but it does not apply to categories Congress singled out for strict substantiation — travel, meals, and vehicle use among them — and it depends on the judgment of whoever is reviewing your return. Our guide to deductions without receipts covers where the line falls.
Do I need to be incorporated to write off business expenses?
No. A sole proprietor or single-member LLC reporting on Schedule C deducts ordinary and necessary business expenses the same way a corporation does. You do not need a business entity, a business licence or a separate tax ID to deduct a legitimate business cost — you need the cost to be genuinely for the business and to be able to show it.
Does a write-off reduce self-employment tax too?
Business deductions on Schedule C reduce your net business profit, and self-employment tax is calculated on that profit — so yes, an ordinary business expense generally reduces both income tax and self-employment tax. That is why business deductions are typically worth more to a self-employed person than the income-tax rate alone suggests. Estimates — confirm with your tax professional.
This guide is educational and describes US federal rules in general terms; state rules and Canadian rules differ, and individual circumstances change the answer. The 50% business-meal limit is per IRS Publication 463 and the digital-records position per Rev. Proc. 97-22. Estimates — confirm with your tax professional.