Period calculators use the information you’ll provide from your last cycle to predict the date for day 1 of your next cycle. Periods aren’t new, people have been collecting info on this for a while and although everybody is unique, we share so much in common.

Let’s say that your last cycle began on August 6 and you want to be prepared for your first week of school. Good plan! August 6th, the first day you bled, will be Day 1 of your cycle, and the first piece of information we enter. Next up you’ll input the number of days you bled for, generally speaking about 4-7. Finally, you’ll be asked for the length of your cycle. On average, menstrual cycles last for 28 days, which means there are 28 days from the first day of one period to the first day of the next. Yours might be shorter or longer (21-35 days) depending on how long you’ve been menstruating, your age, activity level, and other factors besides! The important thing is that you are able to work with the period you have. If you already know this, go ahead and enter it! If this is your first time tracking, start by using the average of 28 days to get an estimate. Tip: if you know the start date of your last two periods, you can count the number of days from day 1 of the earlier period to day 1 of your most recent period. This will give you the length of your menstrual cycle!

To recap, you’ll need:
• The first day of your last period
• How long it lasted.
• The length of your menstrual cycle

The period tracker can also help you calculate your ovulation date! Your date of ovulation is when the egg is released from your ovary. You may have noticed on the calendar that in addition to menstruation being outlined in red, there are also dates outlined in blue. These dates are your peak ovulation days. In a 28-day cycle, the expected date of ovulation is day 14, i.e. two weeks before your next cycle begins. If your cycle is shorter or longer (or if you haven’t been counting every day since your period ended) that date could change and that’s where the period calculator comes in. These dates outlined in blue are your most fertile days, in the event that you’re trying to become pregnant. Once released, the egg can live up to 24 hours while sperm can live for up to 3-5 days.

Average length is about 5 days but remember, there’s always variation! Anything from 3-7 is considered normal. It’s possible that you’ll see light brown discharge for the final few days, so you can try a Human Cherish Pant liner for your lighter flow.

Curious about how long you’ll be using a period calculator? The transition to post-menstrual life begins between 45 and 55 years old.