The Menstrual Cycle and calculating it manually

Trying to conceive is an exciting time in life, but it’s one that can also be confusing and stressful for a couple. There are many factors that play into the chances of getting pregnant in any given month and trying to keep track of all of them can add an extra and unnecessary burden to hopeful mothers.

With a little bit of knowledge and practice, you can learn to calculate the estimated dates for ovulation based on your menstrual cycle.

Understanding your menstrual cycle is one of the most important steps to conceiving because it will tell you when you’re most fertile in a month. This time period is roughly six days out of the month, so it’s important to get the timing right. To calculate this important date range, you first need to understand a few facts about your cycle:


You’ll need to know the length of your average menstrual cycle. This varies from woman to woman, but it’s usually around 28 days, although it can be as short as 24 or as long as 34! The days of your cycle begin and end on the day you first start your period.


Your menstrual cycle is broken into three phases. It’s important that you understand what happens during each phase so you can have the best chance of getting pregnant.

Follicular Phase

This 1st phase of the cycle starts on the first day of your menstruation cycle and it’s when your eggs begin to grow in your ovaries. While many start this growth, typically only one egg will reach full maturity.

During this cycle, your ovaries are also working hard to prepare a place to house the egg. This phase lasts around 15 days and continues right up until ovulation.


The 2nd phase of your cycle is one of the most important parts when it comes to conception. Exactly when ovulation occurs depends on the length of your personal cycle, but it usually happens about halfway through your full cycle.

During ovulation, the fully-grown egg is released from the follicle and the ovary and waits in the fallopian tube to be fertilized by a sperm.

Luteal Phase

The 3rd and final phase occurs after ovulation. If the waiting egg was not fertilized by a sperm, it enters the luteal phase. This is the stage when your period occurs and the unfertilized egg is released from your body.

After Ovulation (if fertilized) – If the egg is to be fertilized, it must take place within 12-24 hours after ovulation, so the sperm has to be in place in order to make it happen. Once fertilized, the egg and sperm form an embryo which then travels to the uterus to implant itself into the uterine wall where it will grow for the next nine months!

Menstrual Cylce Diagram


As mentioned before, determining the timing of your ovulation is critical when you’re trying to conceive. One way to determine this is by using an online calculator like the one found here. However, if you’re concerned about the reliability of those results, you can also calculate your dates manually.

Manually Calculating Ovulation Days


The easiest way to calculate what days you’ll be ovulating is by counting days on a calendar to get a good starting point. The first day of your cycle begins on the first day of your period, so that’s Day One.

The last day of your cycle begins the night before you start your next day period. The number of days in that period gives you the length of your cycle. For this example, let’s say you have a 28-day cycle.

You ovulate roughly midway through your cycle, so if your cycle is 28 days long, you can estimate an ovulation date on Day 14 of your cycle.

If your cycles are closer to 35 days, your ovulation day would be around day 21, so your most fertile days would be days 19-21.

If your cycle is closer to 21 days, your ovulation day would be around day 7 and your most fertile days would be days 5-7. It’s best to have sex every other day starting five days before your ovulation date, as sperm can live up to five days.

Body Temperature

Another way to manually determine if you’re ovulating is by taking your body temperature. This method is much more accurate than looking at a calendar, but you will need a basal temperature thermometer, which you can get at any pharmacy.

Take your temperature every day starting on the first day of your period and plot it on a graph or in your calendar. Before long, you’ll spot a .4F rise in your temperature over three consecutive days.

This occurs about five days before your ovulation date and continues for three days after it. That time period is your best chance for getting pregnant.

Detecting Signs

Another way to know that you’re ovulating is to be familiar with the signs and in touch with your body. Our bodies give out signals when ovulation is nearing, and when it’s passed, all we have to do is be aware of them.

When estrogen levels are highest and ovulation is coming, you’ll notice a stretchy cervical fluid that’s similar to egg whites and your cervix will be high, soft and open.

You can also check your urine for high levels of estrogen using an ovulation predictor kit. Some women even experience ovulation cramping similar to period cramps.

Chances of Getting Pregnant

Tracking ovulation helps in both getting pregnant or in avoiding it. If you want to get pregnant, your fertile window is when you should be having sex. This period reflects the lifespan of sperm, which is 5 days, and the lifespan of the ovum, which is 24 hours.

Having sex six days before you ovulate gives you basically zero chance of getting pregnant due to how long sperm can stay alive. However, if you have sex five days before, your chance rises to 10%.

chance of conception

This percentage will increase the closer you get to ovulation and will then decrease once again after the end of the fertile period. During your fertile days, you should be having sex every 2 to 3 days to increase your chances of conception.

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