If you’re anything like us (or really anyone we know who has ever experienced a period!) you might be familiar with a certain anxious anticipation- what if you get your period on vacation? At school? At your sister’s wedding?

What if we told you it didn’t have to be a surprise? That there are reliable ways to predict your cycle that will take the guesswork out of planning your next big event? We know it came as a huge relief to us so here’s hoping it can help you out, too. Introducing the period calculator. 

Glad you did! Luckily for us menstruators, periods aren’t new. People have been collecting info on this for a while and although every body is unique, we share so much in common. Period calculators use the information you’ll provide from your last cycle to predict the date for day 1 of your next cycle.

A period tracker works by determining the start of your next cycle by placing in the dates from your last cycle. Then, you input the number of days you bled (generally 5-7) and what the typical length of your cycle is. 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. However, your period might be shorter or longer (21-35 days), depending on how long you’ve been menstruating, your age, activity level, and other lifestyle factors! Tip: If you know the start date of your last two periods, you can count the number of days from day one of the earlier period to day one of your most recent period. This will give you the length of your menstrual cycle!4

To recap, you’ll need:

• The first day of your last period
• How many days your period lasted in your last cycle
• 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. In our example above, those dates are August 17-21 and September 14-18. 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 5 days.

Like we said above, the average length is about 5 days but remember, there’s always variation! Anything from 2-7 is considered normal. It’s possible that you’ll see light brown discharge for the final few days, so you can try a Light Days Plus 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, with 51 being the North American average for menopause.

You might also find that the first few years after getting your period will consist of irregular cycles and some spotting. It might take time for your body to find its rhythm, but you should notice a pattern as you get older. Plus, factors like age, diet and exercise, giving birth and breastfeeding could all impact your regularity. If you feel like something is off, always ask your doctor for advice – in the words of Dr. Jessica shepherd no question is too obvious! To learn more, check out our article on irregular periods.

This might take a few cycles but we promise you a period calculator is like that kind friend who loaned you their sweater to hide the stain from the last time your period surprised you. Except of course now you won’t be getting surprised anymore, so you get to be the friend loaning the sweater next time round!