I have been off birth control for four months and want to start again how long will it take before its safe to have sex.?

Soon: Generally, if you start most hormone contraceptives on the first day of your period, you get excellent effectiveness. Full effect with all hormonal contraceptives can be relied on after 1 month.

1 full cycle : We recommend one full pack of pills to be safe. During the first month back on the pill you should use back up contraception such as a condom.