Leviticus 25:50-52

50They and their buyer are to count the time from the year they sold themselves up to the Year of Jubilee. The price for their release is to be based on the rate paid to a hired worker for that number of years.

51If many years remain, they must pay for their redemption a larger share of the price paid for them.

52If only a few years remain until the Year of Jubilee, they are to compute that and pay for their redemption accordingly.