Ovulation Calculator
Estimate your next period, an approximate ovulation date and an illustrative fertile range from your usual cycle.
Do not use this estimate to prevent pregnancy.
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What this can tell you
- Give a calendar-based estimate for regular cycles of 21–35 days.
- Show your own logged cycle lengths (median and range).
What it cannot tell you
It cannot confirm ovulation, give a probability of pregnancy, or work as contraception. Cycles vary, and ovulation can happen earlier or later than any calendar estimate.
How this is calculated
Day 1 is the first day of your period. Estimated ovulation day = cycle length minus 14, so ovulation date = period start + (cycle length − 14 − 1) days. The illustrative fertile range runs from 5 days before to 1 day after that date. Next period = period start + cycle length. Irregular or uncertain cycles, cycles outside 21–35 days, pregnancy, after birth and hormonal contraception do not get a prediction.
Related InfantXmore articles
Sources
- Fertility in the menstrual cycle – NHS (England), England. Checked 19 October 2026 (official entry point). Opens in a new tab.
- Trying to get pregnant? Here’s when to have sex – ACOG, United States. Checked 19 October 2026 (official entry point). Opens in a new tab.
Group: Fertility & reproductive health. Responsible: InfantXmore editorial team (not a clinical review). No clinician endorsement is claimed.
Your data
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