Menstrual Cycle Calculator
Estimate your likely ovulation date, fertile window and next menstrual period from your last period and usual cycle length. These dates are approximate and cannot confirm ovulation.
Enter menstrual cycle information
Estimate upcoming periods using your usual cycle pattern. Dates are predictions, not guarantees.
Menstrual Cycle Calculation Results
Calculation methodology
Next expected period = first day of last period + usual cycle length. Additional periods are projected by adding the cycle length again. Estimated period end date = projected period start + duration - 1 day. Cycle day is counted from the most recent projected period start. Actual timing and bleeding duration can vary.
Frequently asked questions
Can this calculator predict my exact period date?
No. It estimates future dates from your usual cycle length. Actual cycles can vary.
How is cycle length measured?
Count from the first day of one menstrual period to the first day of the next.
What if my cycles are irregular?
Predictions may be inaccurate. Track actual dates and discuss persistent irregularity with a healthcare professional.
What counts as the first day of a period?
Generally the first day of menstrual bleeding, rather than spotting alone.
Does this calculator confirm pregnancy?
No. A late period may have several causes. Use an appropriate pregnancy test if needed.
Can I use predicted dates to prevent pregnancy?
No. Calendar predictions alone are not reliable contraception.
When should I seek medical advice?
Seek medical guidance for very heavy bleeding, severe pain, prolonged absence of periods or other concerning symptoms.
Important health information
This calculator is for general education. Do not use these estimates alone to avoid pregnancy. If your periods are irregular, you have concerns about fertility or need contraception advice, speak with a qualified healthcare professional.