Find your fertile window, ovulation day, and best days to try to conceive — free, no account required.
The fertile window is the period of time each cycle when you can become pregnant. It spans 6 days: the 5 days leading up to ovulation and the day of ovulation itself. Outside this window, conception is extremely unlikely.
The window exists because sperm can survive in the fallopian tubes for up to 5 days, while the released egg lives for only 12–24 hours. Having sex in the days before ovulation means sperm is already waiting when the egg is released.
Studies consistently show conception rates are highest when sex occurs 1–2 days before ovulation. The egg reaches peak fertility right at ovulation but is viable for under 24 hours — sperm needs to be there first.
Ovulation typically occurs 14 days before your next period, regardless of cycle length. So a 28-day cycle means ovulation around day 14; a 32-day cycle means around day 18. The luteal phase (post-ovulation) is relatively fixed at 12–14 days.
A calculator gives you an estimate. To confirm ovulation is actually occurring — and pinpoint the exact day — track your basal body temperature (BBT) and cervical mucus changes. WomensPal lets you log both alongside your cycle data.
Your calculator gives you dates to target, but your body also sends signals when ovulation is near:
Use the first day of your most recent period — that's day 1 of your cycle. If you're unsure, use an approximate date.
Count from the first day of one period to the first day of the next. Track a few cycles to find your average if you're unsure — most cycles fall between 24 and 35 days.
The calculator highlights your full fertile window (6 days) and your peak days (the 3 days with the highest conception probability). Aim for regular sex during the green zone.
Use the WomensPal app to log cervical mucus and BBT alongside your dates. Over 2–3 cycles, patterns emerge that make your fertile window predictions far more accurate than any calculator alone.
WomensPal lets you log BBT, cervical mucus, symptoms, and mood. It predicts your fertile window and gets smarter as you track. No subscription. No paywall.
Start tracking free →It estimates your fertile window using your last period date and average cycle length. Ovulation typically occurs 14 days before your next expected period (cycle length minus 14). The fertile window covers the 5 days before ovulation plus ovulation day itself.
Your most fertile days are the 2–3 days leading up to ovulation and the day of ovulation itself. Sperm can survive for up to 5 days in the reproductive tract, so having sex before ovulation gives the best chance of conception.
Ovulation calculators are a good starting estimate but not a precise tool. Stress, illness, travel, and hormonal changes can shift ovulation by several days. For more accuracy, combine calculator estimates with BBT charting, cervical mucus observation, or OPK strips.
Use your average cycle length as the input, but also track cervical mucus and use OPK strips to detect your LH surge — which directly indicates ovulation is 12–36 hours away. The WomensPal app helps you track all of these alongside your cycle.
It is very unlikely. The egg survives 12–24 hours after ovulation, and sperm can survive up to 5 days. Outside this window, conception is extremely unlikely. If you are trying to avoid pregnancy, do not rely on cycle-based calculations alone — use a reliable contraceptive method.
The most reliable at-home confirmation is a BBT rise of 0.2–0.5°C that persists for at least 3 days. An OPK detecting your LH surge predicts ovulation 12–36 hours in advance. Egg-white cervical mucus is another reliable sign ovulation is approaching.