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
October 4, 2026
~ October 8, 2026
14 days away
🥚Ovulation Day
September 20, 2026
Today
💕Fertile Window
September 15, 2026
~ September 20, 2026
5 days ago
🌙Luteal Phase
September 21, 2026
~ October 4, 2026
1 days away
Cycle Phases
🩸Follicular💕Luteal
Next 3 Cycles Forecast
Cycle 1
🩸
Nov 1
🥚
Oct 18
💕
Oct 13 ~
Cycle 2
🩸
Nov 29
🥚
Nov 15
💕
Nov 10 ~
Cycle 3
🩸
Dec 27
🥚
Dec 13
💕
Dec 8 ~
💡 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.
When does PMS appear and what helps?
It typically shows up in the late luteal phase, about 5-11 days before bleeding starts, and eases once the period begins. Regular sleep, light aerobic exercise, and moderating caffeine and salt are the usual first steps. Logging when symptoms start alongside the predicted dates here reveals your own pattern. If symptoms disrupt daily life, ask a clinician about PMDD.
Results are general estimates and are not a substitute for professional gynecologic medical advice, diagnosis, or care.