Birth Control Switch Protection-Gap Calculator

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Find how many days of backup protection you may need when starting or switching birth control, using current US CDC rules.

Leave blank for the conservative backup rule.

This follows general US CDC start rules. Postpartum, post-abortion, emergency-contraception, missed-dose, and method-specific medical questions need separate advice.
Peer-Reviewed Science
Updated Dec 2025
See Methodology
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Methodology

The calculator applies the CDC's 2024 start windows and backup periods for US contraceptive methods. If the latest-period date is missing or outside the no-backup window, it uses the conservative method-specific backup period.