Period Calculator
Track your menstrual cycle, predict future periods, and identify your most fertile days with our comprehensive period calendar and ovulation calculator.
Period Information
Most periods last 2-7 days. Average is 5 days.
Cycle length is from day 1 of period to day 1 of next period.
A period calculator predicts your future menstrual cycle dates based on your past cycle history. Knowing when to expect your period helps you plan ahead, track regularity, and identify potential health concerns from unusual cycle patterns. This tool estimates your next period date and fertile window based on average cycle length.
Understanding the Menstrual Cycle
The average cycle is 28 days, but normal cycles range from 21 to 35 days. Cycles shorter than 21 or longer than 35 days may indicate hormonal imbalances worth discussing with a healthcare provider. The cycle starts on the first day of full menstrual flow and ends the day before the next period begins.
| Cycle Phase | Days (28-day cycle) | What Happens |
|---|---|---|
| Menstrual | 1-5 | Uterine lining sheds |
| Follicular | 1-13 | Egg follicles develop |
| Ovulation | ~Day 14 | Egg released |
| Luteal | 15-28 | Progesterone rises, then falls |
Cycle Tracking and Health
Regular tracking reveals your unique cycle patterns. Sudden changes in cycle length, flow, or symptoms can be early indicators of conditions like PCOS, thyroid disorders, or perimenopause. Tracking also helps you understand PMS patterns, energy levels, and mood changes tied to hormonal shifts throughout the cycle.
Frequently Asked Questions
Is it normal for my period to be irregular?⌄
Occasional irregularity is common and often caused by stress, illness, travel, significant weight changes, or intense exercise. Consistently irregular cycles (outside the 21-35 day window), very heavy bleeding, or periods that stop altogether are worth discussing with a healthcare provider, as they can indicate underlying conditions.
Can I get pregnant on my period?⌄
It is unlikely but possible, particularly for people with short cycles. Sperm can survive up to 5 days in the reproductive tract. If ovulation occurs early in the cycle (within a week of the period), sperm from intercourse during menstruation could still be present. Pregnancy cannot be ruled out based on menstrual timing alone.
What factors affect menstrual cycle length?⌄
Significant factors include stress (which can delay or suppress ovulation), body weight (very low or high BMI can disrupt hormones), exercise intensity, hormonal contraceptives, thyroid function, age (cycles often shorten as perimenopause approaches), and underlying conditions like PCOS or endometriosis.
How accurate are period prediction apps and calculators?⌄
Predictions based on average cycle length are most accurate for people with very regular cycles. For anyone with natural cycle variation of more than a few days, predictions are estimates with a range of uncertainty. The more historical data you track, the better the prediction accuracy for your individual pattern.