Leviticus 25:27, 51-52

then he shall calculate the years since its sale and refund the balance to the man to whom he sold it, and so return to his property.

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