retroactive
adjective
LAW uk/ˌretrəʊˈæktɪv/ usif a law, decision, etc. is retroactive, it has effect from a date in the past before it was approved:
The changes will not be retroactive.
The Justice Department had opposed the retroactive application of the guidelines.
retroactive to sth The proposed pay raises are retroactive to July 1.
See also
retrospective