Personal checks don’t have a legal expiration date, but in the United States a bank doesn’t have to cash a check that is presented more than six months after the date written on it. Under Section 4-404 of the Uniform Commercial Code (UCC), the model banking law adopted by the states, a bank has “no obligation” to pay an ordinary check presented after that six-month window.
That rule doesn’t make an old check void. The same section says a bank may still choose to pay an older check in good faith and charge the payment to the account holder. Whether your bank will honor a check older than six months is up to the bank, so the safest move is to deposit any check well before that point.
Certified checks are the exception named in the law: the six-month rule in Section 4-404 does not apply to them. If you have an old check that a bank refuses, ask the person or business that wrote it to issue a new one.