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Period Calculator

Estimate your next period date and cycle timeline from your last period date and average cycle length (all estimates).

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Inputs

Cycle-based estimate from LMP + averages.

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Default: 28 days

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Default: 5 days

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Use 0 to skip projections (default: 3).

Ovulation settings (optional)

Enable ovulation and fertile window estimates.

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Default: 14 days

Fertile window is an estimate: sperm may survive up to ~5 days; the egg is viable for ~24 hours.

Results

Predictions for planning (estimates).

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Next expected period

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Enter your cycle details and calculate to see an estimate.

Cycle length used

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Day 1 to next Day 1

Period length used

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Start to end estimate

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How to calculate your next period

A menstrual cycle is commonly counted from the first day of one period to the first day of the next period. This calculator estimates your next period by adding your average cycle length to the first day of your last menstrual period (LMP).

Because real cycles can vary month to month, results are estimates. If your periods are irregular, predictions are less reliable.

Menstrual cycle length explained

Many adults have cycles that fall between 21 and 35 days, but a wider range can still be normal. Tracking multiple cycles helps you estimate a more realistic average.

Ovulation and fertile window explained

Ovulation is often estimated about 10 to 16 days before the next period. A common default estimate for the luteal phase is 14 days. The fertile window is often estimated as the five days before ovulation through about one day after ovulation.

FAQ

Questions people ask

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How do I calculate my next period?

A simple estimate adds your average cycle length to the first day of your last period (LMP). This calculator automates that estimate.

What is a normal menstrual cycle length?

Many adults have cycles between 21 and 35 days, but variability is common. If you’re concerned about significant changes, consider talking to a healthcare professional.

When do you ovulate in your cycle?

Ovulation is often estimated about 10 to 16 days before the next period. For a 28-day cycle, that’s commonly around day 14.

Can a period calculator predict fertile days?

It can provide an estimate of the fertile window around ovulation, but real fertility timing varies—especially with irregular cycles.

Is this period calculator accurate for irregular cycles?

Predictions may be less accurate with irregular cycles. Consider tracking over multiple months or using additional ovulation signs if you need more precision.

Disclaimer

This calculator is for informational purposes only and does not provide medical advice. For personalized guidance, consult a qualified healthcare professional.