Calculators

Health

Using the Period Calculator

The period calculator tells you when to expect your period. Enter information about your cycle and the calculator automatically counts the days for you. See where you are in your cycle and estimate when your period should happen.

You'll need some information about your cycle to use the period calculator:

1. Enter the first day of your last period
2. Enter the typical length of your period
3. Enter your average cycle length. Count from the first day of one period up until the first day of the next.

When you do a calculation the period calculator tells you what cycle day you're currently on. It also estimates when your next period will begin. We provide a calendar feature that shows a preview of your expected period dates 3 months at a time, ahead or in the past. You can also print a list or calendar view of your expected period dates for the next 12 months.

Predict Your Next Period

You can easily calculate when to expect your next period. Use these steps to mirror how the calculator finds the dates.

1. Recall the first day of your last period. Day 1 is the first day of actual flow.
2. Find your average cycle length. Count from day 1 of one period up until day 1 of the next. Track 2–3 cycles to find your average cycle length.
3. Add your cycle length in days to your last period start date. The result is the date of your next expected period. Note that all target dates are estimates as natural cycles may not match calculations using formulas and math.

Example period date calculation: If your last period started on January 1 and your cycle is 29 days long, your next period should start around January 30.

• Add your cycle length to the first day of your last period
• January 1 + 29 Days = January 30

Why Use a Period Calculator

Knowing when to expect your period can help you plan for upcoming events or travel. It can also help inform when you might ovulate. Typically ovulation occurs around 14 days before the start of your next period. This is not a guaranteed ovulation date, but simply an estimate of the ovulation time frame. Just subtract 14 days from your expected period date.

Planning for travel and events: Know when to expect your period so you can pack supplies, plan activities and avoid surprises.

Understanding your body: Notice patterns and symptoms. Knowing your typical cycle can help you recognize shifts or changes in what's normal for you.

Tracking fertility: If you're trying to get pregnant, understanding your cycle helps you figure out when you're most likely fertile.

When tracking your period, print out the calendar forecast and use it mark the first day of each period. You can also record your symptoms and track your flow. Or use a period tracking app to have the information stored for later reference. Regular tracking over a few cycles helps you recognize patterns and notice anything unusual.

Frequently Asked Questions