How to calculate ovulation

Many aspects of human fertility are complicated; others are straightforward and simple. To conceive a baby, a healthy sperm has to meet and fertilize a mature egg. And in a normally functioning menstrual cycle, the mature egg is only available for around 24 hours following ovulation. Considering this,  there is a first question a woman will ask herself, once she’s decided that now is the right time to get pregnant. How do I calculate my ovulation day?

In this blog, we explain how your fertile window of around a week every month works. Why do you need to be able to calculate ovulation days in advance? Why not record them after the event? You can get to know your own personal rhythm to help you understand how to calculate your ovulation date, so you stand the best chance of becoming pregnant.

Understanding your fertility window

When a mature egg is released from your ovary at the point of ovulation, it can only remain viable for around 24 hours. Your fertility window is the time during the month when you could conceive. Then, why is it closer to one week than one day? It’s because sperm can survive inside the body for up to five days. So, if there are already sperm present in the fallopian tubes when you ovulate, the odds of conceiving during that cycle are probably better than if you only had sex the day of, or the day after, you ovulate. Therefore, calculating your ovulation date is a matter of prediction. You can know what your fertile time is likely to be in advance of your day of ovulation.

Research published in Elsevier, the Dutch scientific publishing company, has revealed these statistics about the percentage chance of pregnancy:

• Days 1 to 7 of cycle, including menstruation – your least fertile stage
• Days 8 to 9, after menstruation – a low likelihood of conception
• Days 10 to 14, the days around ovulation – the time you are most likely to conceive
• Days 15 to 16, after ovulation – conception is less likely but still possible
• Days 17 to 28, when your uterus lining thickens, are very much less fertile.

It looks easy, doesn’t it? Knowing that the first day of your period is Day 1, you can calculate that the time between days 10 and 14 is your most fertile period. The above statistics assume a regular 28-day cycle, and the fact is that while some people conform to this Goldilocks average, very many more do not. Your time of ovulation is more accurately calculated as around 14 days before your next period. Therefore, understanding your individual cycle is so important.

How to calculate ovulation in your own cycle

If your menstrual cycle is regular, the arithmetic is not difficult. You subtract 14 days from the day of your next period. So, for example, if your cycle normally lasts for 30 days, you are most probably going to ovulate on Day 16. If your cycle is a shorter one of 24 days, your ovulation date will be around Day 10.

This simple calendar calculation is all well and good if you have a regular cycle. However, it’s worth bearing one thing in mind. Even with a regular cycle, ovulation does not always take place on the same day. And, as a further complication, many people do not have a regular cycle. Also, for some women, although their cycle is regular, they would like the added comfort of being able to predict with a bit more certainty the date of ovulation than is available simply through counting the days. Luckily, there are a few ways that you can do this.

Methods of calculating ovulation

In addition to the calendar method that we’ve described above, there are other ways of calculating your ovulation date. These rely more on subtle signs and signals from your own body. These signs can include a change in the vaginal discharge and an increase in base body temperature. You can also use an ovulation predictor kit. This is a more scientific way of measuring physical changes.

The vaginal discharge method

During your less fertile times, normal vaginal discharge tends to be thick and viscous. During your fertile period, as your body produces more estrogen, vaginal discharge increases in volume and becomes more slippery, something like egg whites.

Increase in body temperature

Your body also produces progesterone when an egg is about to be released. This hormone causes a slight elevation of body temperature. Therefore, the temperature monitoring method can also let you know when ovulation is about to occur. The increase is only very slight, and so accurate measurement is essential. To help this you can take your temperature at the same time every day, usually before getting up in the morning. Alcohol consumption, illness, or a change of contraception can also affect it.

Ovulation predictor kit

An ovulation predictor kit, also known as ovulation tests, can register an increase in luteinizing hormone (LH) which increases in order to trigger the release of an egg in ovulation. The raised levels of LH can be detected in your urine by the predictor kit. Some come in the form of paper test strips which you dip into a container of urine. Others look like pregnancy tests, which you hold in your stream of urine. The results tell you when you are going to ovulate soon, and so this is the signal to have sex for the next two or three days.

What fertility help is available?

If, despite attempts to track your ovulation and time your intercourse for the best chance of conception, it hasn’t happened, it can be a cause of anxiety. But there’s lots of help available in that quest for egg and sperm to meet. There are hormonal treatments that allow us to manage ovulation with accuracy to facilitate straightforward treatments such as Artificial Insemination (AI) or the more complex but highly successful In Vitro Fertilisation (IVF). If you’re feeling concerned about your fertility and want to know more about the help available, do contact us at IVI.