Charles Ellicott Commentary Leviticus 27:23

"then the priest shall reckon unto him the worth of thy estimation unto the year of jubilee: and he shall give thine estimation in that day, as a holy thing unto Jehovah." — Leviticus 27:23 (ASV)

Then the priest shall reckon to him. — In this case, the vower is not to pay the low rate fixed for a field which is the family inheritance , but the priest is to value it in proportion to the number of crops it will produce up to the year of Jubilee, in the same way as fields are valued in ordinary purchases .

And he shall give your estimation in that day. — This valuation the vower or his relatives had to pay all at once, without, however, the additional fifth part of its value; while in the case of vowing an hereditary field, the vower had the advantage of paying the small sum by yearly installments.