Period Calculator

Add your average cycle length to the first day of your last period. If your last period started on the 1st and your cycle is 28 days, your next period is expected around the 29th. This calculator also projects the next few cycles.

Ovulation usually occurs about 14 days before your next period. Because sperm can survive up to 5 days, the fertile window is roughly the 5 days before ovulation plus ovulation day. Cycle-based estimates are approximate — ovulation kits or temperature tracking are more precise.

A typical cycle is 21–35 days, with 28 days often used as an average. Some variation month to month is normal. Consistently very short, very long, or irregular cycles are worth discussing with a healthcare provider.

Calendar prediction alone is not reliable contraception, especially with irregular cycles — typical-use failure rates are significant. Use it for awareness and planning, and rely on a proven contraceptive method if you are preventing pregnancy.

Common causes include stress, travel, illness, significant weight or exercise changes, hormonal shifts, and pregnancy. An occasional late period is usually not a concern, but if periods are frequently irregular or absent, consult a healthcare professional.