Any debts that aren't on your credit report can't hurt your credit score, but you could still be in for a nasty surprise when a creditor shows up at your door demanding money. The credit bureaus don't do their own investigations; they just include the information that gets passed on to them by creditors. So just because the credit reporting agencies don't know about a debt doesn't mean you're not responsible for paying it.
It's true that most creditors share information about their clients' accounts with at least one credit bureau, but that's not always the case. According to the credit agency Experian, there's no legal requirement to pass along information about your debts. For example, if you borrow money from a private school for college, that debt isn't going to show up if the school doesn't tell the credit bureaus. However, even an unreported debt could end up on your credit report if a lender gets a judgment against you in court, since it becomes public information at that point.
Older debts that you haven't made payments on for at least seven years may also be missing from your credit report. According to Experian, the statute of limitations for collecting debt doesn't always match the seven years during which the negative information continues to affect your credit score. For example, if your state has a 15-year statute of limitations before old debts go away, the debt will fall off your credit report long before you're off the hook for ponying up the cash.
The Internal Revenue Service is prohibited from sharing tax debt information with credit bureaus. Strict privacy laws limit what Uncle Sam can share with anyone about your tax information, and that includes how much you owe on your tax bill. However, a tax debt could still find its way onto your credit report if the IRS has filed a lien against your property. At that point, the lien is public information.
If someone provides you a one-time service without setting up a payment plan, that's not going to appear on your credit report. Medical bills are a common example because most hospitals just want you to pay the bill and get on with your life. Since it's not actually a loan, there's nothing to share with the credit bureaus. However, if you don't cough up the money in a timely manner, it could end up in your credit file if the hospital sells the debt to a collections agency. If it gets a legal judgment against you for the amount you owe, that goes on your credit report, too.
Mark Kennan is a writer based in the Kansas City area, specializing in personal finance and business topics. He has been writing since 2009 and has been published by "Quicken," "TurboTax," and "The Motley Fool."