Menstrual Cycle Calculator
This menstrual cycle calculator predicts when your next period is likely to start, estimates your ovulation day and highlights your most fertile window. Simply enter the first day of your last period, how long your cycle usually lasts and how many days your period tends to last, and it instantly maps out your upcoming dates. Whether you are trying to conceive, spacing out plans, tracking your body for health reasons or simply want to avoid being caught off guard, having a clear calendar of your cycle makes life easier. Keep in mind that every body is different: the calculator assumes a regular, predictable cycle, so treat the dates as helpful estimates rather than exact guarantees, especially if your cycles tend to vary from one month to the next.
Next period
Estimated ovulation
Fertile window
Upcoming periods
This result is an estimate based on a regular cycle. Real cycles vary from month to month, and this calculator is not a contraceptive method. If you have doubts, delays or irregular cycles, consult your doctor or gynecologist.
Publicidad
How it works
The calculation follows the standard cycle model. Your next period is estimated by adding your cycle length to the first day of your last period — for a 28-day cycle that means 28 days later. Ovulation is estimated as roughly 14 days before your next expected period, because the luteal phase (the time between ovulation and menstruation) is fairly constant at about two weeks. The fertile window spans from about 5 days before ovulation to 1 day after it, reflecting how long sperm can survive in the reproductive tract and how long the egg remains viable. The calculator repeats the cycle length forward to list your next few expected periods. These are model-based estimates and not a substitute for medical tracking or contraception.
Publicidad
Preguntas frecuentes
- How accurate is a menstrual cycle calculator?
- It is accurate when your cycles are regular and consistent. Because it assumes a fixed cycle length, real cycles that shift by a few days each month will make the predicted dates drift. Track a few cycles to find your true average length for the best results.
- How is my ovulation day estimated?
- Ovulation is estimated as about 14 days before your next expected period, based on the fairly constant length of the luteal phase. If your cycle is 28 days, ovulation lands around day 14; if it is 32 days, around day 18. It is an estimate, not a precise measurement.
- What is the fertile window?
- The fertile window is the range of days when conception is most likely — roughly from 5 days before ovulation to 1 day after. Sperm can survive several days inside the body and the egg stays viable for up to about 24 hours, which is why the window spans several days.
- Can I use this as birth control?
- No. This calculator only estimates dates from a regular-cycle model and does not account for the natural variability of ovulation. It should never be used as a contraceptive method. For reliable contraception, talk to a healthcare professional.
- What counts as the first day of my period?
- The first day of your period is the first day of full menstrual bleeding, not spotting. This is day 1 of your cycle and the reference point the calculator uses to project your next period and ovulation.