Charles Ellicott Commentary Leviticus 25:27

"then let him reckon the years of the sale thereof, and restore the overplus unto the man to whom he sold it; and he shall return unto his possession." — Leviticus 25:27 (ASV)

Count the years of the sale thereof. —To regulate the price of the redemption money, the crops that the purchaser had enjoyed since acquiring the property were valued. This value was deducted from what he originally paid for the plot of land, and the difference was returned to him by the seller, to whom the inheritance reverted.

Thus, for instance, if there were thirty years from the time the purchase was made to the year of Jubilee, and the seller or his next of kin redeemed the inheritance ten or fifteen years after the transaction, he had to return to the purchaser either one-third or one-half of the purchase money when the land was restored to the seller or his next of kin. In the interest of the purchaser, however, it was enacted during the Second Temple that redemption should not take place before he had the benefit of the field for two productive years , and that he could claim compensation for expenses for improvements.

Restore the overplus unto the man to whom he sold it. —That is, an equitable estimate is to be made of what the land is likely to yield from the time of its redemption by the seller to the Jubilee, which is to be credited to the purchaser.