Period calculator
Predictions assume your recent cycles are typical for you. Stress, travel and illness can shift your period by several days.
🔒 Calculated locally — your dates never leave your device
The calendar shows your predicted period days, fertile window and estimated ovulation for the next two cycles, so you can plan ahead.
A variation of a few days is normal. If your period is more than 7 days late, take a pregnancy test first if you are sexually active; if cycles stay irregular for months, talk to a doctor.
Frequently asked questions
How late can a period be and still be normal?
Up to about 7 days of variation is common. If you are sexually active and more than a week late, take a pregnancy test; if delays repeat, see a doctor.
Why does my cycle length change?
Hormones respond to stress, sleep, weight changes, exercise and illness. Occasional shifts are normal; persistent irregularity deserves a check-up.
Can I rely on this calendar for contraception?
No. Cycle predictions are not a contraceptive method. Use reliable contraception if you want to avoid pregnancy.
Related reading
Ovulation bleeding and mid-cycle spotting
Light spotting around ovulation is common and usually harmless. A brief dip in estrogen when the egg is released can cause a small amount of pink or light-brown discharge for a day or two in the middle of your cycle.
Read more →Why is my period late?
A period that is up to about 7 days late is usually normal. If you are sexually active and more than a week late, take a pregnancy test first. Beyond pregnancy, common causes include stress, weight or exercise changes, thyroid problems and PCOS.
Read more →References
- NHS – Periods and fertility in the menstrual cycle
- ACOG – Your First Period / Menstruation FAQs