Miss the deadline, file the wrong amount, or leave out supporting records, and a debt that should have been paid in a bankruptcy case can end up ignored or paid at a lower priority. A proof of claim is the formal written notice a creditor files in a bankruptcy case to say, in effect, "this is what I'm owed, and here is why." It usually lists the amount due, whether the debt is secured or unsecured, and any documents that back it up, such as contracts, bills, judgments, or medical charges.

In practical terms, this filing tells the bankruptcy court, the trustee, and the debtor that the creditor wants to share in whatever distribution the case allows. If no proof of claim is filed when one is required, the creditor may have little or no right to payment through the case. The deadline is often called the bar date, and the timing rules come from the Federal Rules of Bankruptcy Procedure, including Rule 3002 and Rule 3003.

For injury-related claims, a proof of claim can matter when a person hurt on the job or in a crash is owed money by a company or person who files bankruptcy. Medical providers, insurers with liens or subrogation interests, and injured people with pending personal injury claims may all need to pay close attention. If treatment records, wage loss evidence, or claim amounts are incomplete, recovery can shrink fast - never a pleasant surprise.