Period Tracker

Predict next period, fertile window and cycle day from last period and cycle length.

Predictions are estimates based on your saved data (kept private in this browser). Cycles vary naturally — this isn't a substitute for medical advice or pregnancy testing.

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How to use Period Tracker

Three quick steps — no sign-up needed

  1. Step 1

    Enter first day of last period

    Use the start date of your most recent period.

  2. Step 2

    Set cycle and period length

    Average cycle length (about 20-45 days in the form) and period length in days.

  3. Step 3

    Save and read predictions

    See predicted next period timing, fertile window hints, and cycle day based on those averages.

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About Period Tracker

Period Tracker predicts next period timing, cycle day, and fertile-window style estimates from the first day of your last period, average cycle length, and period length. People search "next period calculator", "menstrual cycle tracker", and "period prediction" for this planning view.

Enter last period start, typical cycle length, and how many days bleeding usually lasts, then save to view predictions. The model assumes a relatively regular cycle - the more irregular your history, the wider the uncertainty.

Tracking can help you notice patterns to discuss with a clinician (very short, very long, or suddenly changed cycles). It is not a diagnosis of PCOS, endometriosis, or other conditions, and it is not a standalone birth-control method.

These results are educational estimates only and are not a medical diagnosis. Talk to a qualified clinician for personal health decisions. Seek care for severe pain, flooding, absence of periods, or sudden cycle changes.

Benefits of Period Tracker

Next period estimate Plan around a predicted start based on your averages.
Cycle day context See where you are in the cycle under standard counting.
Fertile window hint Calendar-style fertility context alongside period prediction.
Simple inputs Three fields - no mandatory account to run a basic prediction.

Frequently asked questions

How does period prediction work?

It projects forward from last period start using the cycle length and period length you enter.

What cycle length should I use?

An average over recent months is better than one unusual cycle.

Can this replace a doctor visit?

No. Use it for organisation and discussion, not diagnosis.

Is my data stored?

Follow the site privacy policy for any saved predictions on your device or account.

Is this medical advice?

No - educational cycle estimates only.