Plan B (Emergency Contraception) Calculator
Estimate pregnancy risk after unprotected sex and how much Plan B may reduce that risk based on timing.
Plan B Risk Reduction Estimator
Mobile-friendly quick check: enter intercourse time, dose timing, and cycle details to compare baseline vs reduced risk.
How This Plan B Risk Estimate Works
The model first estimates baseline conception probability from cycle timing (using your LMP and cycle length to infer likely ovulation timing). It then applies a time-to-dose Plan B reduction factor that is strongest early and weaker over time.
Core concept
Residual risk = baseline risk × (1 − Plan B effectiveness)
Because levonorgestrel mainly delays ovulation, effectiveness can be lower if ovulation has already occurred. The tool highlights when alternatives (ella or copper IUD) may be worth discussing urgently.
Important limitation
This is educational, not diagnostic. Individual risk differs by true ovulation date, sperm survival variability, and real-world adherence. For urgent decisions, seek clinical care promptly.
Frequently Asked Questions
Common questions answered by our medical team
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