When is nuvaring effective ?

NuvaRing: If you begin the NuvaRing with your period it should be effective right away. If you start it at any other time use a back up method for at least 7 days. After 7 days the NuvaRing should be fully effective (98 % effective).

Pretty quickly but..: The ring starts working very quickly but you should use a backup method of contraception for a week if you are not switching from another hormonal contraceptive method.