Estimate your fertile window & next period
An estimate only, not a form of contraception or medical advice.
Ovulation usually happens about 14 days before the next period starts, so it falls on day (cycle length minus 14) of your cycle. Sperm can survive up to about five days, so the fertile window runs from five days before ovulation to the day after. Cycles vary month to month, so treat these dates as approximate.
It gives a good estimate for regular cycles. Irregular cycles make calendar methods much less reliable.
No. Calendar estimates are not reliable contraception.
No. The calculation runs entirely in your browser and nothing is sent anywhere.
Body mass index & health status
Exact age in years, months & days
Daily calorie needs (TDEE / BMR)
Healthy weight range for your height
Your 5 training zones from max & resting HR
Daily protein target for your weight & goal