Leviticus 25:50-54

50He is to calculate with the one who bought him, from the year that he sold himself to the Year of Jubilee, and the price of his sale will be in proportion to the number of years. Like the days of a hired worker it will be with him.

51If there are still many years, in proportion to those he is to reimburse the price of his redemption from his purchase price.

52If there remain only a few years until the Year of Jubilee, then he shall calculate with him in proportion to his years of service he is to reimburse the price of his redemption.

53He will stay with him as a hired worker, year by year. But he is not to rule with harshness over him in your sight.

54Even if he is not redeemed by these means, then he will still be released in the Year of Jubilee—he and his children with him.