Menstrual Cycle Calculator
Predict your next period, ovulation window, fertile days and cycle phases for the next 6 cycles.
Your Cycle Information
Phase Legend
Next 6 Cycles
About Menstrual Cycle Tracking
What is a menstrual cycle?
A menstrual cycle begins on the first day of a period and ends the day before the next period starts. The average cycle is 28 days, but a healthy range is 21–35 days. The cycle has four phases: menstrual, follicular, ovulation and luteal.
How is ovulation date calculated?
Ovulation is estimated by subtracting the luteal phase length from the cycle length:
Example: Day 1 + (28 − 14) = Day 14
The luteal phase (from ovulation to next period) is typically 12–14 days and is the more consistent half of the cycle. The follicular phase varies more between individuals.
What are fertile days?
The fertile window spans the 5 days before ovulation plus the day of ovulation itself — 6 days total. Sperm can survive up to 5 days in the reproductive tract, so intercourse before ovulation can result in fertilisation.
This calculator uses a standard ±5/+1 day window around the estimated ovulation day. Actual fertility varies.
What is the PMS window?
PMS (premenstrual syndrome) symptoms typically occur in the 5–7 days before a period starts, during the late luteal phase. This calculator marks the 5 days before the expected period start as the PMS window.
Why does my cycle vary month to month?
Cycle length can vary due to stress, illness, significant weight change, travel, hormonal changes, perimenopause and many other factors. A variation of ±3 days is common and considered normal. Consistent irregularity should be discussed with a healthcare provider.