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Period Calculator

Next period dates, cycle phases and a twelve-month calendar.

Calculators Reviews Free · no sign-up

This cycle, phase by phase

The next twelve periods

#StartsEndsDays away

Predictions further out are progressively less certain, because a few days of variation between cycles is entirely normal and the error compounds. The twelfth date is a rough guide, not a date to plan around.

Next period starts

—

Right now

Days until next period—
Cycle day—
Current phase—
Ovulation this cycle—

—

Periods in the next twelve months

Cycle length is counted from the first day of one period to the first day of the next; 21 to 35 days is typical for adults. Stress, illness, travel, weight change, medication and hormonal conditions all shift timing. Everything is calculated in your browser and no cycle data is stored or sent anywhere.

Quick Tool Overview

The Period Calculator predicts your next twelve periods from your last one and your usual cycle length, and breaks each cycle into its menstrual, follicular, ovulatory and luteal phases so the calendar shows what is happening, not just when bleeding starts.

What it does
Predicts twelve upcoming periods and maps cycle phases
You give it
Last period date, cycle length and period length
You get back
Next period dates, days remaining and phase breakdown
Best for
Planning around your cycle without installing an app
Calculators Free, unlimited use No sign-up Runs in your browser

About the Period Calculator

Predict your next twelve periods from the date your last one started and your usual cycle length. Each cycle is broken into its four phases — menstrual, follicular, ovulatory and luteal — so the calendar shows what is happening rather than only when bleeding starts.

Cycle length is normally counted from the first day of one period to the first day of the next, and anything from 21 to 35 days is considered typical for adults. Variation of a few days between cycles is entirely normal, so predictions further out are progressively less certain — the twelfth predicted period is a rough guide, not a date to plan around. Everything is calculated in your browser, and no cycle information is stored or sent anywhere.

Key features of the Period Calculator

Twelve months ahead

A full year of predicted dates, with a note that confidence drops the further out you look.

All four phases mapped

Menstrual, follicular, ovulatory and luteal, so each cycle is legible rather than just a start date.

Days until next period

The single number most people open a period tracker to find, shown first.

Normal ranges stated

21 to 35 days is typical for adults, and the page says that a few days variation between cycles is normal.

Nothing is stored

No account, no tracking, no cycle data leaving your browser — unlike most period apps.

How to use the Period Calculator

  1. 1

    Enter your last period

    The first day of bleeding.

  2. 2

    Set cycle and period length

    Cycle length is first day to first day; period length is how many days you bleed.

  3. 3

    Read the next dates

    Your next period, the days remaining, and a twelve-month projection.

  4. 4

    Check the phases

    Each cycle is split into menstrual, follicular, ovulatory and luteal phases.

Frequently asked questions

Add your average cycle length to the first day of your last period. On a 28-day cycle starting the 3rd, the next period is expected around the 31st.

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