How this ovulation calculator works
This ovulation calculator estimates the day you ovulate as 14 days before your next period. From your last period start, it adds your cycle length to find your next period, then counts back 14 days for ovulation. The fertile window is the six days from five days before ovulation to one day after.
For day-to-day tracking, a colour-coded calendar and saved predictions, open the full Sakhi period & ovulation tracker. Like this calculator, everything stays on your device.
Frequently asked questions
How does an ovulation calculator work?
It estimates ovulation as roughly 14 days before your next expected period. The luteal phase (ovulation to period) is fairly consistent, so counting back from the next period gives a reasonable ovulation estimate.
What is the fertile window?
The fertile window is about six days: the five days before ovulation plus the day of ovulation and the following day. Sperm can survive several days and the egg lives about a day, so these are the days with the highest chance of pregnancy.
How accurate is it?
It is an estimate. Real ovulation can shift with stress, illness or irregular cycles. For trying to conceive or to avoid pregnancy, combine it with other signs and speak to a doctor — calculators alone are not a contraceptive method.
Is my information saved or uploaded?
No. This calculator runs in your browser and does not send your dates anywhere. Nothing is stored unless you choose to log it in the full tracker, which also stays on your device.