ret·ro·ac·tive 
/ˌrɛtroʊˈæktɪv/ adjective
/ˌrɛtroʊˈæktɪv/ adjective formal : effective from a particular date in the past
▪ They all received a retroactive pay raise. ▪ The new tax will be retroactive to January 1.
▪ They all received a retroactive pay raise. ▪ The new tax will be retroactive to January 1.
— ret·ro·ac·tive·ly adverb
▪ The new law will be applied retroactively.
▪ The new law will be applied retroactively.
