What this tool is for

This calculator gives you a quick estimate of when you are likely to ovulate, along with the days in your cycle when you are most likely to conceive. It is a simple way to map out the coming weeks so you know roughly when to focus on trying for a baby.

It is not a medical test and it cannot confirm ovulation on its own, but it is a useful starting point if you want a clearer picture of your cycle without tracking temperatures or buying test kits.

Who it suits

It is aimed at anyone in the UK who is trying to conceive, or thinking about starting soon, and wants a plain overview of their fertile window. It works whether your cycle runs to the textbook 28 days or sits anywhere between about 21 and 35 days, as long as your periods are reasonably regular.

If your cycles are very irregular, if you have a condition such as PCOS or endometriosis, or if you have been trying for a while without success, the results here should be treated as a rough guide only. In that case it is worth speaking to your GP or a fertility specialist for proper advice.

How it works

You enter the first day of your last period and your average cycle length. The calculator then works out your predicted ovulation date, the five days leading up to it, and the day after, which together make up your fertile window. You get the results on screen straight away in plain English, with no account needed and no personal details saved. You can come back and run it again next month with updated dates if you want to keep an eye on how your cycle is shifting.

Remember that ovulation can move by a few days from one month to the next, even in a steady cycle. Treat the dates as a helpful window rather than a fixed appointment, and pair them with how you actually feel during the month for a fuller sense of what is going on.