Period Calculator
Track your menstrual rhythm: predict upcoming period start dates, see where you are in your current cycle, and know when your next fertile window opens.
Current cycle day
Day 1
Next period expected
Tuesday, September 22, 2026
Following period
Tuesday, October 20, 2026
Then again around
Tuesday, November 17, 2026
Next fertile window opens (~ovulation −5d)
Thursday, September 3, 2026
Predictions assume a regular cycle. Stress, travel, illness and contraception can shift dates by several days.
How to Use the Period Calculator
- Enter the first day of your last period.
- Add your average cycle length and how many days bleeding usually lasts.
- View predicted dates for your next three periods plus current cycle-day position.
Formulas Used
Average cycle length = mean of your last 3-6 cycles
Next period ≈ last period start + average cycle length
Follicular phase: day 1 to ovulation | Luteal phase: ~14 days before next period
Frequently Asked Questions
What is a normal cycle length?
Anywhere from 21 to 35 days counted from the first day of one period to the first day of the next is considered regular for adults.
When should I worry about a late period?
A few days of variation is normal. If your period is more than a week late and pregnancy is possible, take a test; cycles absent for three months warrant medical review.
Why did my prediction miss?
Cycles shift with stress, sleep, travel, illness, weight change and hormonal contraception - the calculator averages history but cannot foresee these factors.
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