Leviticus 25:48-52

then he shall have redemption right after he has been sold. One of his brothers may redeem him,

or his uncle, or his uncle’s son may redeem him, or one of his blood relatives from his family may redeem him; or if he prospers, he may redeem himself.

He then, with his purchaser, shall calculate from the year when he sold himself to him up to the year of jubilee; and the price of his sale shall correspond to the number of years calculated. It is like the days of a hired worker that he will be with him.

If there are still many years remaining, he shall refund part of his purchase price in proportion to them for his own redemption;

but if few years remain until the year of jubilee, he shall so calculate with him. In proportion to his years he is to refund the amount for his redemption.