Calculator
How it works and when to use it
Ovulation usually happens about 14 days before the next period, so the calculator takes 14 days off your next period to estimate it.
The fertile window is the five days before ovulation and the day of ovulation itself, since sperm can live for several days while the egg can be fertilised for a short time only.
Reference: Ovulation ≈ next period − 14 days (luteal phase assumed 14 days); fertile window: Wilcox AJ, Weinberg CR, Baird DD. N Engl J Med 1995;333:1517-21
Frequently asked questions
How accurate is it?
It is an estimate for a regular cycle, real ovulation can come earlier or later from one cycle to the next even in regular cycles, and home ovulation tests or ultrasound follow-up find it more precisely.
Can I rely on it for contraception?
No, it is not a method of contraception, ask your doctor about the method that suits you.
When should I see a doctor about not getting pregnant?
After a year of regular trying without a pregnancy, after 6 months if you are 35 or older, or earlier if your cycles are irregular or there is a known cause.
Tools you may also need
- Pregnancy and due date calculator Your estimated due date and how far along you are today.
- Period calculator The dates your next periods start and end.
- Body mass index (BMI) calculator Your BMI, its class and the healthy weight for your height.
- Calorie calculator Maintenance calories, the calories for your goal and the time to reach it.
- Ideal weight calculator The lowest and highest healthy weight for your height, and what to lose or gain.
- Body fat percentage calculator Body fat from a tape measure, and fat mass in kilograms.
Clinic software for this specialty
Try Clinicato for your clinic
These calculators are free here for everyone, and in Clinicato 49 medical tools work inside the patient's file with the "Medical tools" add-on: filled from the visit and the vital signs, with the result added to the visit's plan, next to appointments, prescriptions and invoices.