How to use Ovulation and Period Calculator
- Enter the first day of your last period.
- Enter your average cycle length.
- Read the predicted ovulation day, fertile window and next periods.
About this tool
Ovulation usually happens about 14 days before the next period, so it is estimated as the cycle length minus 14 days. The fertile window is the five days before ovulation plus the day itself, because sperm can survive for several days.
Cycles vary from month to month, so these dates are estimates and not a reliable method of contraception. This calculator gives general estimates from standard formulas and is not medical advice. Talk to a doctor or dietitian about your own health.
Frequently Asked Questions
- What is a normal cycle length?
- Between 21 and 35 days, with 28 days being the average.
- Can I use this to avoid pregnancy?
- No. Predictions can be off, so use a reliable contraception method.
Related tools
- Pregnancy Due Date CalculatorEstimate your due date and current stage of pregnancy.
- Add or Subtract Days from a DateFind the date that is a number of days, months or years before or after another date.
- Steps to Distance CalculatorTurn a step count into distance, using a stride length estimated from your height.
- Macro CalculatorTurn a calorie target into daily grams of protein, carbs and fat.
- Running Pace CalculatorFind your pace per kilometer or mile, and estimate finish times at the same pace.
- BMI CalculatorCheck your body mass index and the healthy weight range for your height.