What is a Pregnancy Calculator?

The pregnancy calculator is a tool that calculates various components of pregnancy, mainly used to determine the due date (estimated date of delivery) and the current pregnancy week. It calculates the estimated due date from the date of conception, or first day of your last menstrual cycle (LMP), the date of an early pregnancy test, or the date of an early pregnancy ultrasound, or, for in vitro fertilization (IVF) or artificial insemination (AI) pregnancies, the embryo transfer date.

These calculators aren’t powered by state-of-the-art equations (in most cases, they use the average length of human gestation, which is 280 days, or 40 weeks, from the first day of a woman’s last menstrual period), but they do provide a general guide to what happens when: Due date (and baby’s arrival), trimesters, fetal development stages. They are commonly employed by pregnant women and their care providers to determine the progress of pregnancy and to plan prenatal care.

How to Calculate Pregnancy?

Main Methods to Calculate Pregnancy and Due Date

A. By LMP (Last Menstrual Period)

• This is the easiest and most widely used method, particularly for women with regular menstrual cycles.
• The magic happens on the first day of your last menstrual period, which, even though you generally are not pregnant at this point, is being counted as “day one” of pregnancy because that’s when your body begins preparing to make a baby.
• The traditional way is to add 280 days to the first day of your last menstrual period (LMP) to estimate your due date.

Naegele’s Rule:

• Take the first day of your LMP and add 7 days.
• Subtract 3 months.
• Add 1 year.
• Example: Your last menstrual period began on January 1, 2025:
• Add 7 days → January 8, 2025
• Minus 3 months → October 8, 2024
• Add 1 year → October 8, 2025 (your estimated due date) 1, 2025.
  • Add 7 days → January 8, 2025
  • Subtract 3 months → October 8, 2024
  • Add 1 year → October 8, 2025 (estimated due date).

B. According to the Date of Conception

• So if you find the precise date of conception (if, for instance, you tracked your fertility symptoms with CycleBeats or used IVF), you can shit for an EDD by adding 266 days (or 38 weeks) to that date.
• This approach is not frequently employed because few women know exactly when they conceived.

C. Based on Ultrasound

• An early pregnancy ultrasound (8–12 weeks) can be used to obtain a more reliable estimate of gestational age and EDD if the LMP is unknown or cycles are irregular.
• The ultrasound measures the fetus (crown-rump length) and estimates gestational age based on the Nagele formula.

D. IVF or Assisted Reproduction

• For pregnancies achieved via in vitro fertilization (IVF), the due date is calculated based on the date of embryo transfer:
  • Day-3 embryo IVF or Assisted Reproduction.WriteHeader / MainBodyIVF or Assisted ReproductionPage ContentLike medications alone, IVF treatment increases the likelihood of twins or multiples.
  • Cycles with in vitro fertilization (IVF). For pregnancies resulting from in-vitro fertilization (“IVF”), use the patient’s egg retrieval date as the LMP (Last Menstrual Period).
  • Transfer date: 3-day embryo – Due date is 263 days from transfer.
  • Embryo transfer on Day 5: Expected date of delivery is 261 days post-transfer.

Using a Pregnancy Calculator

• Put in the first day of your last period or browse by entering another crucial date (conception, ultrasound, egg retrieval, embryo transfer).
• It will calculate your estimated due date and the time of your gestation.
• Some calculators even remind you of what’s going on with your baby and your body, as you progress week by week!

Important Notes

• Your due date is an estimate; only about 4 percent of babies are born on the date they’re due, though most are born within two weeks before or after.
• If you don’t have regular cycles or you’re not sure when your LMP was, an early ultrasound could give you the most accurate due date.
• Always check with your doctor and a specialist for confirmation and individualised advice.

Table of Pregnancy Calculation