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Ovulation Calculator

Knowing when you are ovulating increases your chances of getting pregnant.

Our handy ovulation calculator is a good way to get started. It will help you work out when you should next try to conceive. You may not always need a fertility monitor, but if you do our calculator will also tell you which is best for your individual circumstances if you are looking to take more control of your fertility. If you need help to answer the questions there's more information below the calculator.

Understanding The Results

What's the difference between a 'regular' and 'irregular' cycle?

Your 'cycle' is the number of days from the start date of one period to the start date of your next period. If that number of days is about the same from one cycle to the next (within 1-4 days) and more often than not you have almost no variation in the number of days, then you have 'regular' cycles and it's easy to calculate your average number days in your cycles. If your cycle length varies 5 days or more from one cycle to the next, and particularly if you find that cycles rarely have the same number of days, then you have a degree of 'irregular' cycles. Don't worry though, most women can conceive naturally even if they have irregular cycles, they just need a little more help.

When is the Fertile Window?

Your fertile window is governed by two important factors: how long an egg survives when it's released from one of your ovaries, and how long sperm can survive in your body.

An egg survives 24-48 hours after you’ve ovulated, while sperm can survive for up to five days in the body. So you have a fertile window of 6-8 days in each cycle when egg and sperm can successfully meet and you can get pregnant.

How do I understand my Fertile Window?

Everyone is unique, and that means you have to find out answers about your own body and cycle to understand when best to try for a baby. Around 30% of women ovulate in the middle of their cycle, but Wilcox et al. (2000) estimated that 2% of women were in their fertile window by the fourth day of their cycle and 17% by the seventh day, and around 30% ovulate more than 2/3rds of the way through the cycle.

Any kind of irregularity in your cycle makes it all the more important to take advantage of those times when you do ovulate, which means careful tracking of your cycle to spot the key signs that give you a clue when you’re in your fertile window.

[1] The key publication outlining the accuracy and positive predictive value of advance prediction of ovulation was shown at the 2014 ESHRE meeting: Papaioannou S, Delkos D, Pardey J (2014).
[2] The accuracy of ovulation confirmation by OvuSense is based on the data set originally published at the 2013 ASRM meeting as a quality index: Papaioannou S, Aslam M (2013), and developed in [1]
[3] Internal Fertility Focus side by side study of OvuFirst and OvuCore Sensors (2021), documented as a class II medical device in the notified body reviewed CE Certificate Technical File.

What should I look for in my cycle patterns?

Click on each of the cycle pattern images below to find out more - for each image we answer the questions:

  • What is it?
  • How common is it?
  • Why does it happen?
  • How can I see it?.
  • What does it mean?
  • What can be done about it?