Colleen Mulvihill, PhD

About this project

I conceived the idea for this project when I was trying to conceive. As the months dragged on without a positive pregnancy test, I dug into the scientific literature after being frustrated by conflicting, anecdotal-based information about return to fertility after birth control.

In the scientific literature I also found conflicting, incomplete information and studies with poor data quality. I built this tool to provide the best possible current estimate on when someone might expect to conceive based on current highest quality studies.

Methodology & limitations

This calculator synthesizes data from two large prospective studies:

• Yland et al. (2020) — Pregravid contraceptive use and fecundability. BMJ. N=17,954. Provides method-specific delays in fertility return, defined as cycles until the fecundability ratio returns above 0.90 relative to barrier method users.
• Wesselink et al. (2017) — Age and fecundability in a North American preconception cohort study. Am J Obstet Gynecol. N=2,962. Provides age-specific fecundability ratios adjusted for education, BMI, smoking, and other confounders, with separate estimates for nulligravid women.

All estimates are population averages. Individual fertility varies substantially based on factors this calculator cannot assess, including cycle regularity, underlying conditions (PCOS, endometriosis, thyroid function), partner fertility, and others.

If you have been trying to conceive for more than 12 months (or 6 months if over 35), consider consulting a healthcare provider.