6 Bad Debt Rules That Decide When You Can Write Off an Unpaid Invoice
Sam's List Editorial | 2026-08-15
A client stops paying. You send four emails, then a demand letter, then nothing. Eventually you clear the invoice out of your accounting system and assume you will at least get a tax deduction out of it.
Most business owners are wrong about that. The bad debt write off rules do not care how frustrated you are or how obviously uncollectible the invoice looks. They care about your accounting method, the year the debt became worthless, and what you can document.
Here are the six rules that decide whether that unpaid invoice is a deduction or just a loss you absorb quietly.
1. If You Are on Cash Basis, There Is No Deduction
This is the rule that surprises people most, and it is the one that applies to the largest number of small businesses.
A cash-basis business recognizes income when it gets paid. If a client never pays, you never recorded the income. There is nothing to deduct, because you were never taxed on it in the first place. Writing it off in your bookkeeping software feels like something happened. On the return, nothing did.
The economic loss is real. The tax deduction is not. Those are two different things, and conflating them is how owners end up expecting a refund that never arrives.
2. Accrual Businesses Deduct Only What They Already Recorded as Income
Accrual-basis businesses are in a different position. You recognized the revenue when you invoiced, you paid tax on income you never collected, and IRC Section 166 generally allows a deduction for a business bad debt that becomes worthless.
The deduction is limited to your basis in the debt, which for a normal receivable is the amount you already took into income. You cannot deduct the profit you would have made, the interest you never charged, or the opportunity cost of the work.
One practical implication: if you switched from cash to accrual mid-stream, only receivables recorded under accrual are eligible.
3. Worthlessness Belongs to a Specific Year, and You Have to Pick It
The deduction is allowed in the year the debt becomes wholly worthless, not the year you decide to stop caring about it. That timing is a genuine trap, because the IRS position is that you claim it when worthlessness occurred, and claiming it late can mean claiming it in a closed year.
What establishes worthlessness is facts, not feelings. A client that filed Chapter 7. A judgment you cannot collect on. A business that dissolved. A collection agency that returned the file. Aged silence alone is weaker evidence than most owners assume.
Partial worthlessness has its own rule. A business can deduct a partially worthless debt only to the extent it charges off that portion on the books during the year, which means the bookkeeping entry has to happen in the year you want the deduction.
4. Booking the Write-Off Is Not the Same as Deducting It
Two different systems are running at once, and they do not agree by default.
For financial reporting, GAAP uses the allowance method: you estimate uncollectible accounts and record a reserve, which smooths the expense across periods. For tax, the specific charge-off method applies to most businesses: you deduct particular debts when they become worthless.
An allowance is an estimate, and estimates are not deductible. If your books carry a $40,000 allowance for doubtful accounts, none of that is a tax deduction until specific invoices are identified and charged off.
Running one method and assuming it serves both purposes is the most common reason a year-end schedule does not tie out. This is exactly the kind of reconciliation an outside firm catches quickly. Iota Finance, founded in 2022 and working with clients remotely nationwide, lists SMB owners, VC-backed startups, real estate investors, and high net worth individuals among its specialties, and receivables hygiene sits squarely in that kind of engagement.
Iota Finance has 13 verified client reviews on Sam's List as of 2026-06-26. Each review is submitted by an individual who identifies as a client of the firm and rates it on communication, subject-matter knowledge, and overall satisfaction. Reviews reflect those individual experiences, do not represent an endorsement by Sam's List, and are not indicative of future results.
5. Documented Collection Effort Is What Makes the Write-Off Defensible
You do not have to sue everyone who stiffs you. You do have to show a reasonable effort, and reasonable is judged against the size of the debt.
For a $600 invoice, a documented sequence of statements, emails, and a final demand is usually proportionate. For a $60,000 invoice, an examiner will expect more: a collection agency, a lawyer's letter, or a judgment. Effort that is cheaper than the debt is the standard nobody writes down but everyone applies.
Keep the trail in one place. The invoice, the contract, the dated collection attempts, and whatever ended the pursuit. A file assembled two years later under audit pressure is worth far less than one built as it happened.
6. If a Written-Off Invoice Gets Paid Later, It Is Income Now
Recovery happens more often than people expect. A bankruptcy trustee distributes something. A former client turns their business around and settles old debts. A collection agency succeeds after you gave up.
Under the tax benefit rule, a recovered amount is generally income in the year received, to the extent the earlier write-off produced a tax benefit. You do not amend the old return. You pick it up now.
That is not a reason to delay a legitimate write-off. It is a reason to keep the record, because you need to know how much benefit you actually took before you can figure out how much of the recovery is taxable.
What This Looks Like in Practice
Bad debt is a symptom before it is a deduction. Receivables aging past 90 days are usually the visible end of a scoping problem, a contract problem, or a collections process that nobody owns.
Fix the upstream part and the write-off question stops coming up as often. Deposits on new work. Payment terms that a client agrees to in writing before the work starts. A dunning process that runs on a schedule instead of on your mood.
If your aging report has invoices you have quietly stopped counting on, that is the conversation to have with your accountant this quarter, not next March. You can compare firms by specialty and verified review count in the Sam's List accountant directory.
Frequently Asked Questions
Can I write off an unpaid invoice on my taxes? Only if you are on the accrual method and already recorded the invoice as income. Accrual businesses can generally deduct a business bad debt in the year it becomes worthless under IRC Section 166. Cash-basis businesses get no deduction, because the income was never recognized.
What proof do I need to write off a bad debt? Enough to show the debt became worthless and that you made a reasonable effort to collect. Keep the invoice, the contract, dated collection attempts, and any external evidence such as a bankruptcy notice, a returned collection file, or an uncollectible judgment. The larger the debt, the more effort an examiner will expect.
What is the difference between the allowance method and the charge-off method? The allowance method estimates uncollectible accounts as a reserve and is used for financial reporting under GAAP. The specific charge-off method deducts identified debts when they become worthless and is what most businesses use for tax. Estimates are not deductible, which is why the two rarely match without a reconciliation.
What happens if a customer pays after I wrote the debt off? The recovery is generally taxable income in the year you receive it, to the extent the original write-off gave you a tax benefit. You do not go back and amend the earlier return. Keep records of what you deducted so you can calculate the taxable portion correctly.
About the author: Kimberly Green is the cofounder of Sam's List, where business owners and high earners find vetted CPAs, financial advisors, and fractional CFOs. She's met one-on-one with 400+ financial professionals and writes from the real data behind thousands of client-advisor matches. Ask her anything about finding an accountant - she's heard it all, including the questions people are afraid to ask.