Next period
next period start = last period start + average cycle length
Menstrual Cycle Calculator
Predict your next period, ovulation & fertile window
21 days40 days
2 days10 days
Today is — Day 15 of cycle
Fertile
🩸Next Period
August 1, 2026
~ August 5, 2026
14 days away
🥚Ovulation Day
July 18, 2026
Today
💕Fertile Window
July 13, 2026
~ July 18, 2026
5 days ago
🌙Luteal Phase
July 19, 2026
~ August 1, 2026
1 days away
Cycle Phases
🩸Follicular💕Luteal
Next 3 Cycles Forecast
Cycle 1
🩸
Aug 29
🥚
Aug 15
💕
Aug 10 ~
Cycle 2
🩸
Sep 26
🥚
Sep 12
💕
Sep 7 ~
Cycle 3
🩸
Oct 24
🥚
Oct 10
💕
Oct 5 ~
💡 Health Tips
- •A normal menstrual cycle ranges from 21 to 35 days.
- •Ovulation typically occurs around day 14 of the cycle, but varies per person.
- •The fertile window spans from 5 days before ovulation to ovulation day itself.
- •If your cycle is irregular or painful, consult a healthcare professional.
This calculator assumes a typical cycle. Do not use it for medical purposes.
Cycle prediction starts with last period date, average cycle length, and period duration
This calculator estimates the next period, ovulation day, fertile window, luteal phase, and the next three cycles from the last period start date, average cycle length, and period duration. It is useful for planning when cycles are regular, but stress, illness, sleep, weight change, and medication can shift timing.
Calculation basics
Ovulation
estimated ovulation = next period start - 14 days
Fertile window
from 5 days before ovulation through ovulation day
How to use
- Enter the first day of the last period.
- Set average cycle length and period duration.
- Use the next period, ovulation, fertile window, and three-cycle forecast as planning references.
Frequently asked questions
What is a typical cycle range?
Adult cycles often fall around 21-35 days, but your own usual pattern matters most.
Can this be used as birth control?
No. Ovulation can shift, and calendar prediction alone cannot reliably prevent pregnancy.
What if cycles are irregular or painful?
Repeated irregularity, heavy bleeding, or severe pain may need evaluation by a healthcare professional.
Results are general estimates and are not a substitute for professional gynecologic medical advice, diagnosis, or care.