Due Date Calculator

due date calculator

The due date calculator assists expecting mothers in determining their due date. You can easily estimate your baby’s due date with our tool. In the following article, you will learn about the pregnancy due date and how to calculate it using various methods (Naegele’s rule and conception date).

You’ll also learn about the meanings of terms like LMP etc. Continue reading to learn how to use our due date calculator to determine your baby’s birthday.

The due date calculator uses the first day of your menstrual cycle and the average length of your menstrual cycle to provide three key pieces of information for determining the date of your pregnancy:

  • Date of ovulation (probable)
  • The period of fertility
  • Expected completion date (approximately 266 days from conception)

Formula For Due Date Calculator

We have basically two methods for calculating due date.

1. Last Menstrual Period Is Used To Determine the Due Date

 There are a few other techniques, or guidelines, to calculate a pregnancy’s due date using the latest menstrual cycle. For more precise results, the following instructions are variants on the basic formula. Simply, the more data you have to work with, the more precise the due date will be.

Continue reading if you want to learn more about advanced formulas and how to calculate an accurate due date with them.

a) Naegele rules

The most common method for determining a pregnancy’s due date is naegele rules. We can also calculate the due date using Naegele’s rule as the fundamental rule.

The typical formula goes like this:

LMP +280 days

Ovulation occurs day 14th of a typical menstrual cycle, which can last anywhere from 20 to 45 days.

b) Mittendorf- Williams Rule

The more details you provide, the more accurate the results will be. Mittendorf-Williams’ rule is considered more advanced than Naegele’s rule.

This guideline is based on a study that discovered that first pregnancies take somewhat longer (an average of 288 days after LMP) than subsequent pregnancies (an average of 283 days).

  • First, figure out when your previous menstrual period began.
  • Next, go back three months in time from that day.
  • Finally, if this is your first pregnancy, add 15 days to that date; if this is not your first pregnancy, add 10 days.

The formula is:

LMP-3months+15 days

c) Parikh rule

The predicted delivery date for irregular cycles is calculated using Parikh’s approach, which involves adding nine months to the most recent menstrual period, removing twenty one days, and then adding the duration of past cycles.

The formula is:

LMP+280 days -21 days + the length of the previous cycle

Although this calculation is a variation of Naegele’s rule, it significantly minimizes the risk of making a mistake when calculating your predicted due date.

d) Wood’s rule

Wood’s method considers a woman’s menstrual cycle duration and the number of pregnancies she has had.

You Begin By Calculating Your EDD.

  • For 1ST pregnancies formula is:

LMP + 12 Months- (2months and 14 days) = EDD

  • For successive pregnancies formula is:

LMP + 12 Months- (2months and 18 days) = EDD

Then, In the Formulae Below, You Use the Predicted Due Date.

  • For cycles that go longer than 28 days, use the following formula:

EDD + (real cycle duration–28 days) Equals EDD

  • For cycles that are less than 28 days, use the following formula:

EDD–(28 days–real cycle duration) = EDD

2. Due Date Based On The Day Of Conception

You’d assume that multiplying your conception date by 266 days would give you your due date, but it’s a little more difficult than that. Even if you know the specific day of intercourse, you virtually never know the actual date of conception. What is the logic behind this?

Because determining the exact date of ovulation and hence the date of conception can be difficult. Sperm can survive for up to 5 days in the female body, while the egg can survive for up to 24 hours after being discharged from the ovary.

As a result, conception might happen several days following unprotected intercourse.

LMP in due date calculator

The word “last menstrual period” is abbreviated as “LMP.” Pregnancies are traditionally counted in weeks, beginning with the first day of the woman’s last menstrual cycle. Furthermore, the LMP is the 1st day of your last menstrual period (the start of bleeding) before becoming pregnant. Our calculator calculates the due date using this information. A woman is considered six weeks pregnant two weeks after her first missed period, according to this method of counting.


From the 1st day of your last menstrual period, pregnancy lasts an average of 280 days (40 weeks) (LMP). Even though you didn’t probably conceive until approximately two weeks later, the first day of your LMP is considered day one of pregnancy (fetal development lags two weeks behind your pregnancy dates). Our due date calculator will assist you in determining your exact deadline.


What if I’m not sure when my last menstrual period was?

This happens more often than you might expect. When you can’t recall the initial day of your LMP, there are several options for determining your due date:
1. If you know when you had your LMP, your doctor can estimate your due date based on that.
2. Your doctor may perform an ultrasound to determine your due date if you don’t remember when your last menstruation was.

Why is the ultrasound date different from my due date?

When a doctor does an ultrasound, they create a report that includes two estimated due dates and the results. The date of the LMP is used to compute the first date. However, the ultrasound measures will determine the second date. It’s rare that these dates coincide.

When your doctor looks at the ultrasound results, they’ll see if the dates match up. Unless the due date differs significantly from your ultrasound, your doctor is unlikely to change it.
If you get more ultrasounds, each one will give you a new due date based on the most recent measurements. Measurements from a second- or third-trimester ultrasound should not be used to affect a projected due date.

Early in pregnancy, it’s easier to predict your due date. Later ultrasounds are useful for establishing if the pregnancy is growing normally, but not for estimating the fetus’s age.

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