backdate
🇺🇸
/ˌbækˈdeɪt/
🇬🇧
/ˌbækˈdeɪt/
to write an earlier date on a document than the actual date it was made
The company decided to backdate the contract to the day we first discussed it.
to make something, such as a payment, effective from an earlier date
The raise in salary was backdated to the beginning of the year, so she received the extra money for the past months too.