How long do you have to pay a bill before they can change interest?

The time frame for a billing cycle before interest rates can change varies by the type of bill and the terms outlined in the agreement. Typically, for credit cards, interest rates may change if payments are not made on time, usually after a grace period of 30 days. Utilities and loans may also have specific terms that define how long you can go before incurring interest penalties. Always check the specific terms and conditions of your agreement for precise details.