Due date calculator

Only 5% of women actually deliver their babies on their estimated due date. The reason for this is that your due date is an estimation of when your baby is going to be born. Two factors go into determining your due date, the first day of your last menstrual period or your date of conception and the length of your menstrual cycle. Your due date is calculated by adding 40 weeks or 280 days to the first day of your last menstrual period. However, you can increase the accuracy of your due date by knowing how long your menstrual cycle is and how long your luteal phase is.

Your menstrual cycle is made up of three parts. Moreover, in order to properly use a due date calculator you are going to need to know about all three parts of your menstrual cycle and how they work within the due date calculation. Here is a closer look at all three phases of your menstrual cycle.

Phase one: Follicular phase
This phase begins on the first day of menstruation and lasts until the first day of ovulation. The follicular phase is where the growth or maturation of the egg is taking place inside the follicle, which is a small sac where the egg matures. The follicular phase can also be determined by the first full day of menstrual bleeding. The follicular phase usually lasts between 3 and 5 days, however it can be more or less. During this cycle, the body is preparing for ovulation by releasing a hormone called Follicle Stimulating Hormone. This hormone is designed to stimulate an ovarian follicle to grow and an egg to mature.

Phase two: Ovulation
This phase usually begins around the 14th day of the cycle and is the shortest of all the phases. During ovulation, estrogen causes the lining of the uterus to grow and the cervical fluid to change. The reason that ovulation occurs is due to an increase of the luteinizing hormone. The body responds to the surge of the hormone by releasing an egg from the ovary after the follicle bursts, which usually happens 24 to 36 hours after the surge of the luteinizing hormone. During ovulation, your body also produces progesterone, which is used to increase the blood vessels to the lining of the uterus and prevent other eggs from developing. Progesterone also causes your Basal Body Temperature to rise by about half a degree. The reason that these changes take place is your body is preparing your uterus for a fertilized egg to live in for the next 9 months. It is during ovulation that the egg is fertilized for a pregnancy.

Phase three: Luteal phase
If you have charted your fertility cycles before you are probably well aware of your luteal phase and are aware of the fact that you can use it to increase the accuracy of your estimated due date. However, most women do not chart their luteal phase when trying to conceive because they are mainly concerned with when they ovulate. Your luteal phase is most commonly referred to as days past ovulation. The luteal phase is the time span that occurs after you have ovulated and continues until the day before your next menstrual cycle begins. For woman with regular cycles, the luteal phase is from 10 to 16 days, with the average length being 14 days. During the luteal phase if the egg is fertilized the body is going to start releasing the hCG hormone, which is what pregnancy tests use to detect if you are pregnant. If your body begins, producing hCG this will increase the production of progesterone. This increase in progesterone is important because it is what keeps the uterus intact so that your body can carry out the pregnancy. If there is, no increase in progesterone the corpus luteum dies, so the menstruation cycle begins again.

Here is a look at the different types of due date calculators that are available for you to use.

Number one: Reverse pregnancy calculator
This type of calculator asks you what day you would like your baby to be born on. It uses the estimated due date as a way to tell you when you should start conceiving so that your baby can be born as close to that day as possible. This allows you to avoid certain seasons while being pregnant, some women do not want to deliver babies in the winter months because of weather conditions making it hard to get to a hospital nor do some women want to be almost due in the hottest months of the year because of how uncomfortable they get in the heat. With this calculator, all you need to do is subtract 266 days or 38 weeks from the due date that you have chosen. However, keep in mind that you can only conceive on certain days so the due date that you have chosen might not work for you because the day you would have to conceive does not fit into your cycle.

Number two: Last menstrual period
This type of calculator bases your due date on Naegele's rule. This rule is that a pregnancy is considered to last 280 days or 40 weeks from the date of your last menstrual period. The one thing that you need to know about this rule is that you are not pregnant for the full 40 weeks. Instead, your gestation period is considered 266 days or 38 weeks from the date of conception. How this due date is calculated is that you take the date of your last menstrual period and add 280 days to that, which will result in your estimated due date.

Number three: Approximate conception date
This calculator also uses Naegele's rule because it figures your due date based on 266 days or 38 weeks from the date of conception. This calculator works by making two different calculations. The first calculation that it makes is your approximate conception date based on your last menstrual period. It calculates the due date by using the average number of days in your cycle and your luteal phase. It then adds 266 days to your conception date to get your estimated due date for the second calculation. The formula that is used is (last menstrual period + average cycle length in days) - luteal phase in days = Approximate date of ovulation.

Something to keep in mind is that under Naegele's rule, your ovulation date is also considered the date that you conceived. Naegele's rule also assumes that you have a 28-day cycle and a 14-day luteal phase. This means that ovulation would occur on the 14th day of your cycle. However, all women are different so you will need to track your own cycles and luteal phases to get a better idea of your due date if using this type of calculator. Most calculators based on date of conception allow you to change the length of your cycle and your luteal phase to provide you with accurate results.

Number four: Specified conception date
This type of calculator can only work for people who have a good idea of when they conceived. All that you need to do is add 266 days or 38 weeks to the date that you conceived on and you will get your estimated due date. This is also a great calculator to use if you just want to play around with the different dates of your cycle to see what would happen down the road, basically a great what if calculator.

If you plan to use any type of due date calculator then you are going to need to learn about your menstruation cycle. You are going to need to know the lengths of the different phases so that you can calculate your due date as accurately as possible. The best way to determine your menstrual cycle is to keep a menstrual chart or use computer software that is designed for tracking your menstrual cycle. If you do not want to mess with charting your cycle, you can also write down the first day of your period on your calendar or in a diary. You can also write down the last day of your cycle, which is the last day of your period. By counting from your last day of your period to the first day of your next period, you can get a better idea of how long your menstrual cycle is, even though you will not know the lengths of the various phases.

Regardless of which calculator that you use 95% of women will not give birth on their due date because it is only an estimated date. The accuracy of your due date can increase with the more information you know about your menstrual cycle, but it is still just a best estimate. Most doctors will tell you that there is an error of caution of about two weeks before your due date or two weeks after your due date.