When the next one is due
Enter the first day of your last period, your cycle length, and how long bleeding lasts.
- Next expected11/24/2026
- Following period 112/22/2026 (Tuesday)
- Following period 201/19/2027 (Tuesday)
- Following period 302/16/2027 (Tuesday)
- Following period 403/16/2027 (Tuesday)
How to predict your next period
A menstrual cycle starts on the first day of bleeding and ends the day before the next period begins. Adding your usual cycle length to the start date of your last period gives the expected date of the next.
Once you have the expected date, you can estimate ovulation, about 14 days earlier, and the fertile window. If the date has passed and nothing has started, see the late period calculator.
What is typical for a cycle
| Trait | Typical range for adults | Outside the range |
|---|---|---|
| Cycle length | 21 to 35 days | Shorter than 21 or longer than 35 days |
| Variation between cycles | A few days | Swings of more than about 7 to 9 days point to irregular cycles |
| Length of bleeding | 2 to 7 days | More than 7 days |
Irregular cycles are common in the first years after the first period and in the years before menopause. Hormonal birth control also changes the bleeding pattern.
Irregular cycles: what changes
When cycles swing by more than a week, a fixed-date prediction misses often. The average cycle tab shows how much your recent cycles vary and averages them. Logging dates for several months improves the estimate.
- See a doctor for very irregular cycles, very heavy bleeding, or more than 3 months with no period.
- Stress, weight changes, intense exercise, thyroid problems, and PCOS can change the cycle.
- The predicted date is an estimate and does not replace medical care.
Go deeper
Frequently asked questions
How do I calculate when my next period is due?
Add your cycle length to the first day of your last period. A period that started October 20 with a 28-day cycle is due November 17.
How long is a normal menstrual cycle?
For adults, ACOG calls 21 to 35 days typical. A 28-day cycle is the textbook average, not a rule.
How do I track an irregular cycle?
Write down the first day of at least three periods, figure the gaps between them, and average the gaps. The average cycle tab does that math and shows how much the gaps differ.
How many days does a period last?
Most periods last 2 to 7 days. A period that runs longer than 7 days, or is very heavy, deserves a call to a doctor.
Can a period be late if I am not pregnant?
Yes. Stress, schedule changes, weight shifts, hard training, and hormone changes can all delay a period. If there was unprotected sex, a pregnancy test settles the question.
What is the difference between a cycle and a period?
The period is the bleeding itself, usually 2 to 7 days. The cycle is the whole span from the first day of one period to the day before the next.
Sources and review
- American College of Obstetricians and Gynecologists (ACOG): Menstruation in Girls and Adolescents, and The Menstrual Cycle.
- FIGO (International Federation of Gynecology and Obstetrics): classification system for abnormal uterine bleeding (Munro et al., 2018).