Period
Calculator

Predict upcoming menstrual periods, ovulation dates, and fertile windows based on cycle length and last period date.

Cycle Settings

days
days

Next Period

Dec 2, 2026

Current Cycle Day

Day 1

Legend

PeriodMenstruation days
OvulationEstimated ovulation
FertileFertile window

Predictions

Cycle 1
Period
Dec 2, 2026 – Dec 6, 2026
Ovulation
Dec 16, 2026
Fertile Window
Dec 11, 2026 – Dec 16, 2026
Cycle 2
Period
Dec 30, 2026 – Jan 3, 2027
Ovulation
Jan 13, 2027
Fertile Window
Jan 8, 2027 – Jan 13, 2027
Cycle 3
Period
Jan 27, 2027 – Jan 31, 2027
Ovulation
Feb 10, 2027
Fertile Window
Feb 5, 2027 – Feb 10, 2027
Cycle 4
Period
Feb 24, 2027 – Feb 28, 2027
Ovulation
Mar 10, 2027
Fertile Window
Mar 5, 2027 – Mar 10, 2027
Cycle 5
Period
Mar 24, 2027 – Mar 28, 2027
Ovulation
Apr 7, 2027
Fertile Window
Apr 2, 2027 – Apr 7, 2027
Cycle 6
Period
Apr 21, 2027 – Apr 25, 2027
Ovulation
May 5, 2027
Fertile Window
Apr 30, 2027 – May 5, 2027

Learn more

How do cycle trackers predict ovulation, and why do cycle lengths vary?

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Frequently Asked Questions

Add your average cycle length in days to the first day of your last period to estimate the start of the next cycle. A typical cycle length is 28 days, but cycles ranging from 21 to 35 days are considered normal.

The average menstrual cycle is 28 days, measured from the first day of one period to the first day of the next. Cycle lengths between 21 and 35 days are medically considered within the normal range.

Period calculators are most accurate for people with consistent cycle lengths. Stress, illness, weight changes, and hormonal factors can shift the actual start date by several days from the prediction.

Period Calculator - Menstrual Cycle Predictor | ToolsCanvas