Printed on 3/17/2026
For informational purposes only. This is not medical advice.
This period calculator estimates your next menstrual period start date from the first day of your last period, your average cycle length, and your typical period length. It also shows your current cycle day, estimated ovulation timing (use [Ovulation Calculator](/tools/ovulation-calculator) for detailed fertility planning), and a projected fertile window for planning and cycle awareness.
Formula: Next period start = LMP + n x cycle length; ovulation estimate = next period - 14 days
Your result provides an estimated next period date and your current cycle day. If your cycles are usually regular, the prediction can be useful for planning. If your cycles vary month to month, focus on the approximate window rather than a single exact date.
The tool also estimates ovulation and the fertile window from cycle timing assumptions. If your goal is conception timing, use the [Ovulation Calculator](/tools/ovulation-calculator) for focused fertile-window planning. If pregnancy is possible, the [Pregnancy Due Date Calculator](/tools/pregnancy-due-date) can estimate gestational timing from your last period, and track progress with [Gestational Age Calculator](/tools/gestational-age).
Use this tool for cycle planning, symptom tracking, travel planning, or understanding where you are in your cycle today. It is useful for people with regular or moderately variable cycles who want a quick estimate without a full tracking app.
It can also support preconception awareness when combined with an [Ovulation Calculator](/tools/ovulation-calculator), especially if you are trying to understand when fertility is most likely in upcoming cycles.
This calculator assumes that future cycles resemble your average past cycle length and that ovulation occurs about 14 days before the next period. Real cycles can vary, especially with irregular menstruation, polycystic ovary syndrome (often associated with obesity - assess with [BMI Calculator](/tools/bmi-calculator)), recent postpartum changes, perimenopause, or hormonal contraception changes. Optimize reproductive health with cardiovascular assessment ([ASCVD Risk Calculator](/tools/ascvd-risk)).
Predictions are not diagnostic. Missed periods, very frequent periods, heavy bleeding, or persistent cycle irregularity should be evaluated clinically rather than managed with prediction tools alone.
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
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