effective date
Refers to the date on which a law, contract, regulation, or agreement comes into force.
新しい法律の発効日は来年の四月一日です。
The effective date of the new law is April 1st next year.
契約書に発効日を明記してください。
Please clearly state the effective date in the contract.
Compound of 発効 (hakkou, 'coming into effect') and 日 (hi/bi, 'day').