A good IOU is short, specific, and signed. To write an IOU that will actually protect you, put the full legal names of both parties, the exact amount owed, the reason for the debt, the repayment schedule, any interest, what counts as default, and both signatures onto a single dated document. Everything below is about getting those pieces right so the paper works if you ever need it to.
The Core Elements Every IOU Needs
Start with the full legal names and current addresses of both the borrower and the lender. Use the name that appears on a driver’s license or government ID, not a nickname. If a dispute ever lands in front of a judge, you need to prove exactly who signed.
State the amount owed in both words and numbers: “One Thousand Dollars ($1,000.00).” Writing it twice makes the figure much harder to alter later, and if the two ever disagree, courts generally treat the written-out amount as controlling. If the debt is for goods or services rather than cash, describe what’s owed in enough detail that a stranger reading the document could identify it.
Include two dates: the date the IOU is created and the date repayment is due. The creation date establishes when the obligation began, which matters later for statute-of-limitations purposes. A due date matters even more. Without one, the lender can technically demand repayment at any time, but that ambiguity makes enforcement messier and gives the borrower room to argue they were never actually late.
Add a plain acknowledgment of the debt in the borrower’s voice. Something like: “I, [Borrower’s Name], owe [Lender’s Name] the sum of [amount] for [reason], to be repaid as follows…” Naming the reason isn’t strictly required, but it heads off later arguments about what the money was for.
Spelling Out Repayment
You have two basic structures: a single lump-sum payment by a set date, or installments over time. Pick one and describe it precisely.
For a lump sum, name the date. For installments, spell out the amount of each payment, how often it’s due, and when the schedule starts and ends. “Monthly payments of $200 on the first of each month, beginning April 1, 2026, until paid in full” leaves nothing to interpret. Language like “when I can” or “as soon as possible” is practically unenforceable, because there’s no moment at which the borrower is clearly in breach.
It also helps to say how payment will be made: cash, check, bank transfer, a specific payment app. That way partial payments can be tracked to a record, and neither party can later claim a payment did or didn’t happen.
Interest and Usury Limits
If you’re charging interest, write down the rate, whether it’s simple or compound, and how often it accrues. Without a written interest rate, the debt generally accrues no interest at all.
Every state caps how much interest a private lender can charge. These usury limits typically range from about 10% to 36% depending on the state. Going over the cap is not a small technicality. Consequences range from forfeiting all the interest to having the entire agreement declared void, and in some states charging usurious interest is a criminal offense. Check your state’s limit for personal loans before you settle on a number.
The Zero-Interest Trap
Lending at no interest feels generous, but it can create a tax problem for the lender. When you lend at a rate below the IRS’s Applicable Federal Rate, the IRS can treat the missing interest as if you had earned it, and tax you accordingly. For March 2026, the short-term AFR is 3.59% annually.1Internal Revenue Service. Rev. Rul. 2026-6 There is an exception for gift loans of $10,000 or less between individuals, as long as the borrower doesn’t use the money to buy income-producing assets.2Office of the Law Revision Counsel. 26 USC 7872 – Treatment of Loans With Below-Market Interest Rates For anything larger, either charge at least the AFR or know what you’re taking on.
Default, Acceleration, and Collateral
Define what counts as a default in the document itself. Is it one missed payment? Two consecutive missed payments? Failing to pay by the final due date? Write it in.
Then state the consequences. The most useful provision is an acceleration clause: if the borrower defaults, the entire remaining balance becomes due immediately. Without acceleration language, you’d technically have to sue for each missed installment separately as it comes due.
For larger debts, you can name specific assets the borrower pledges as security. A vehicle, a piece of equipment, electronics. Describe the collateral clearly enough that it can’t be confused with anything else, including serial numbers, makes, and models where they apply, and state that the lender can claim the item if the borrower defaults. Note that secured interests in real property or vehicles usually require separate legal filings to be enforceable against third parties, which is beyond what a simple IOU can do.
Governing Law if You Live in Different States
If the borrower and lender are in different states, add a sentence naming which state’s laws govern the agreement. That single line decides which state’s usury cap, statute of limitations, and contract rules apply, and it heads off a jurisdictional fight before it starts.
Signatures, Witnesses, and Notarization
Both parties should sign and date the IOU, using the same names that appear in the body of the document. The borrower’s signature is the essential one, because it proves they acknowledged the debt. Having the lender sign too confirms both sides agreed to the same terms.
Witnesses aren’t legally required for most IOUs, but they strengthen the document. If the borrower later claims they never signed or were pressured, a witness who isn’t related to either party can testify otherwise.
Notarization goes further. A notary public verifies each signer’s identity and confirms the signing was voluntary. Courts tend to give more weight to notarized documents because the notary’s seal makes claims of forgery or misunderstanding much harder to sustain. For loans of more than a few thousand dollars, the trip to a notary is worth it.
Electronic Signatures
Under federal law, an electronic signature carries the same legal weight as a handwritten one. The E-SIGN Act provides that a contract cannot be denied enforceability solely because it was signed electronically.3Office of the Law Revision Counsel. 15 USC 7001 – General Rule of Validity If you’re drafting over email or through a digital signing platform, both parties should keep the signed electronic file. For anything you might realistically need to enforce in court, though, a notarized paper document is still the strongest footing.
Keeping the Document and the Deadline to Enforce It
Both parties should keep a signed copy. The lender should hold the original, since that’s the primary evidence of the debt. Scan or photocopy it before it goes anywhere. An IOU is worthless if you can’t produce it when you need it.
You also can’t wait forever. Every state sets a deadline for filing a lawsuit to collect on a written agreement, typically between three and six years, though some states allow up to ten or more.4Consumer Financial Protection Bureau. Can Debt Collectors Collect a Debt Thats Several Years Old? Once that window closes, you lose the ability to sue even on a clearly valid debt. In many states, a partial payment by the borrower restarts the clock from the date of the last payment. That can help a lender whose borrower has been paying sporadically, and it’s something a borrower on an old debt should know before making a small “goodwill” payment.
When an IOU Isn’t the Right Tool
An IOU is a signed acknowledgment of a debt. A promissory note is its more formal cousin: it contains an unconditional promise to repay on specific terms and follows a recognized structure under commercial law. Courts generally treat promissory notes as stronger evidence of a binding obligation, because they go beyond acknowledging the debt and commit the borrower to a defined repayment plan.
For a small personal loan between people who trust each other, an IOU is fine. If the loan is large, runs over a long timeline, carries interest, or is secured by collateral, use a promissory note instead. The more specific your IOU is, the closer it functions to a promissory note in practice, but the label matters when the amount does.
Mistakes That Undermine an Otherwise Good IOU
The biggest mistake is vagueness. “John owes me some money” is barely better than nothing. A judge needs specifics: who, how much, when, and on what terms. The second biggest mistake is not getting a signature at all. Beyond those, a few pitfalls come up again and again:
- No due date, which makes it hard to prove the borrower is actually in default.
- An interest rate above the state usury cap, which can void the interest or the whole agreement.
- Only one copy in existence, so a lost original destroys the evidence.
- Oral changes to the written terms, which are easy to dispute and hard to prove. If you agree to reschedule or reduce payments, write it down and have both parties sign the change.
An IOU doesn’t have to be long. It has to be specific. Fifteen minutes of careful drafting when the money changes hands is what makes the document worth anything later.