How the fertile window works
An egg lives for about a day after ovulation, but sperm can survive for up to five days. That makes the fertile window the five days before ovulation and the day of ovulation itself. The best chance of pregnancy is from intercourse in the two or three days before ovulation.
Ovulation usually happens about 14 days before the next period. In a 28-day cycle that is around day 14; in a 32-day cycle, around day 18.
When the calculator is less reliable
- Irregular cycles, where the length changes by more than a week from month to month
- PCOS, where ovulation may not happen every month
- Soon after stopping hormonal contraception, or while breastfeeding
Ovulation test kits or follicle-tracking scans give a more accurate picture.
When to see a fertility specialist
See a specialist after 12 months of regular unprotected intercourse without pregnancy, or after 6 months if you are 35 or older. Come sooner if your periods are very irregular or absent, or if there is a known problem such as endometriosis or a previous pelvic infection.
Questions
How often should we have intercourse to conceive?
Every two to three days through the cycle covers the fertile window without needing exact timing. Daily intercourse around ovulation is also fine.
Can I get pregnant outside the fertile window?
It is unlikely but possible, because ovulation can shift from cycle to cycle.
What if my cycles are irregular?
The calculator cannot predict ovulation reliably. Follicle-tracking scans show when you ovulate, and very irregular periods are worth checking with a doctor.