Guides
Plain-language answers, cited to established medical sources.
How to calculate your next period date
Learn the exact formula behind period prediction: find day 1, measure your cycle length, add it to your last period date — with worked examples and accuracy tips.
Why is my period late? 10 common causes
A late period is usually not an emergency. The 10 most common causes, when to take a pregnancy test, and the signs that mean you should see a doctor.
This tool provides estimates for personal planning only and is not a substitute for professional medical advice, diagnosis or treatment. Predictions must not be used as contraception. If you have concerns about your cycle, heavy bleeding, severe pain or missed periods, please consult a licensed clinician.