Menstrual Cycle Calculator
Track your cycle and predict your next periods, ovulation date, and fertile window based on your last period and average cycle length.
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Your Menstrual Cycle Results
Pregnancy is most likely if you have intercourse during this window.
Upcoming Cycle Forecast
Free Menstrual Cycle Calculator
Use this free menstrual cycle calculator to track where you are in your cycle and predict your upcoming periods, ovulation date, and fertile window. Enter the first day of your last period along with your average cycle and period length to see a full forecast.
A typical menstrual cycle moves through four phases: the menstrual phase (when bleeding occurs), the follicular phase (as your body prepares an egg), ovulation (when the egg is released), and the luteal phase (leading up to your next period). Cycle lengths vary widely between individuals, so use your own average rather than a generic 28-day assumption for the most useful predictions.
How to Use the Menstrual Cycle Calculator
- Enter the first day of your last period.
- Enter your average cycle length and typical period length.
- Click Calculate My Cycle.
- View your current cycle phase, next periods, ovulation date, and fertile window instantly.
Features
- Shows your current cycle day and phase at a glance.
- Forecasts your next three expected periods.
- Estimates your ovulation date and fertile window.
- Mobile-friendly with print, share, copy, and download options.
Frequently Asked Questions
How does this calculator predict my next period?
It adds your average cycle length to the first day of your last period, repeating this for each upcoming cycle to forecast future periods.
What are the four phases of the menstrual cycle?
The menstrual phase (bleeding), the follicular phase (egg development), ovulation (egg release), and the luteal phase (the time between ovulation and your next period).
Why might my actual cycle differ from the prediction?
Stress, illness, travel, medication, and many other factors can shift ovulation and period timing. This calculator gives a statistical estimate, not a guarantee, especially if your cycles are irregular.
Is this calculator free?
Yes, this menstrual cycle calculator is completely free to use with no sign-up required.
Method and Sources
This calculator predicts future periods by adding your average cycle length to the first day of your last period, repeated for each upcoming cycle. Ovulation is estimated as 14 days before each predicted period, and the fertile window as the five days before ovulation plus ovulation day.
Cycle length naturally varies; cycles between about 24 and 38 days are generally considered typical for adults. Stress, illness, travel, and medication can all shift your timing, so treat these predictions as estimates.
Sources:
- U.S. Office on Women's Health — Your Menstrual Cycle
- Mayo Clinic — Menstrual Cycle: What's Typical, What's Not
- Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation. New England Journal of Medicine, 1995
This calculator is for general information only and is not medical advice. Read our Calculation Methodology and medical disclaimer.
Related Calculators
Want to know your exact average cycle length from past periods? Try our cycle length calculator. Focused specifically on ovulation? Use the ovulation calculator. Need a day-by-day fertility breakdown? Check the fertile window calculator. Trying to figure out when you conceived? Use the conception date calculator. Already expecting? Try our pregnancy due date calculator. Want to check whether your luteal phase is short, normal, or long? Try the luteal phase calculator.