Pregnancy Due Date Calculator

Calculate your estimated due date, gestational week, and trimester dates from your last period, conception date, or IVF transfer date.

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Please enter the required details and click Calculate.

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Calculation Examples

Calculation Case Result
Last period: January 1 (28-day cycle) Due date: October 8
Last period: January 1 (35-day cycle) Due date: October 15
Conception date: May 15 Due date: February 5 (next year)
IVF 5-day blastocyst transferred on June 1 Due date: February 17 (next year)
Mihail Doncenco
Mihail Doncenco Site Creator & Calculator Expert

Founder and developer of CalcMate. Builds and maintains every calculator on this site, focusing on formula accuracy and clear, practical results.

How to Calculate Your Due Date

The calculator uses Naegele's Rule, the standard obstetric shortcut for a 280-day (40-week) pregnancy counted from the first day of your last menstrual period (LMP): \[\text{EDD} = \text{LMP} + 7\text{ days} + 9\text{ months}\] Example: an LMP of January 1 gives an estimated due date (EDD) of October 8. The rule assumes a 28-day cycle with ovulation on day 14. If you know your ovulation or conception date, the tool counts 266 days from it instead. For IVF, enter the transfer date and the embryo age: the due date is 261 days after a 5-day blastocyst transfer and 263 days after a 3-day embryo transfer.

Understanding Your Pregnancy Timeline

Gestational age counts from the first day of your LMP, so you are already about 2 weeks pregnant at conception. ACOG divides pregnancy into three trimesters: up to 13 weeks 6 days, 14 weeks 0 days to 27 weeks 6 days, and 28 weeks 0 days to birth. It also defines full term as 39 weeks 0 days to 40 weeks 6 days, with early term before that (37 0/7 to 38 6/7) and late term after (41 0/7 to 41 6/7), and post-term from 42 weeks (ACOG Committee Opinion 579, 2013).

Typical milestones: cardiac activity shows on a transvaginal ultrasound around week 6, the nuchal translucency scan runs from 11 weeks to 13 weeks 6 days, and the anatomy scan falls around weeks 18 to 22. Many first-time mothers feel movement between weeks 18 and 25, and often earlier in later pregnancies.

A due date is an estimate. Only about 4 to 5% of babies arrive on their EDD. A first-trimester ultrasound measuring crown-rump length (CRL) is the most accurate way to date a pregnancy. Under ACOG Committee Opinion 700 (2017), the due date moves to the ultrasound date if it differs from the LMP date by more than 5 days up to 8 weeks 6 days, or by more than 7 days from 9 weeks 0 days to 13 weeks 6 days. Discuss your timeline with your obstetrician or midwife.

Stages of prenatal development by trimester

Useful Tips 💡

  • Count day 1 from the first day of full bleeding, not spotting. A one-day error moves the EDD by one day.
  • With irregular cycles or an uncertain LMP, use a confirmed ovulation date or a positive ovulation test. A 35-day cycle pushes the EDD 7 days later than the standard calculation.
  • Confirm the date with a first-trimester dating ultrasound. CRL measurement is accurate to about 5 to 7 days.

📋Steps to Calculate

  1. Enter the first day of your Last Menstrual Period (LMP).

  2. Adjust for your average cycle length if it differs from the standard 28 days.

  3. Click "Calculate" to view your estimated due date, current gestational week, and trimester breakdown.

Mistakes to Avoid ⚠️

  1. Counting pregnancy as 9 calendar months. A full term of 40 weeks is about 9 months and 1 week.
  2. Using the date of intercourse as the conception date. Sperm can survive in the reproductive tract for up to 5 days, so conception may happen several days later.
  3. Skipping the cycle adjustment. A 24-day cycle moves the EDD 4 days earlier, and a 35-day cycle moves it 7 days later.
  4. Reading the EDD as the day labor will start. Only about 4 to 5% of babies are born on it.

Practical Applications📊

  1. Schedule screenings: with an LMP of January 1, the nuchal translucency window (11 weeks to 13 weeks 6 days) runs from March 19 to April 8 in a non-leap year.

  2. Mark the milestones: with the same LMP, the third trimester begins at week 28 on July 16, and the EDD is October 8.

  3. Track weight gain: the US Institute of Medicine (2009) recommends a total gain of 12.5 to 18 kg for a pre-pregnancy BMI under 18.5, 11.5 to 16 kg for 18.5 to 24.9, 7 to 11.5 kg for 25 to 29.9, and 5 to 9 kg for 30 or more (single pregnancy).

Questions and Answers

Can I use this calculator for IVF or assisted reproductive technology pregnancies?

Yes, enter the transfer date and the embryo age instead of the LMP. The due date is 261 days after a 5-day blastocyst transfer and 263 days after a 3-day embryo transfer, because both are 266 days minus the embryo age (266 - 5 and 266 - 3). Example: a 5-day transfer on June 1 gives February 17 the next year. Frozen embryo transfers use the same math, since the embryo age sets the date. IVF dating is usually tighter than LMP dating because the fertilization date is known, and your clinic will still confirm it by ultrasound.

How accurate is a due date calculator for predicting actual delivery?

Only about 4 to 5% of babies are born on their EDD, so treat the date as the middle of a window. ACOG defines early term as 37 0/7 to 38 6/7 weeks, full term as 39 0/7 to 40 6/7, late term as 41 0/7 to 41 6/7, and post-term as 42 0/7 and later (Committee Opinion 579, 2013). A calculator cannot see your cycle details, so a dating ultrasound before 14 weeks gives the most reliable gestational age and may change the LMP-based date.

How do you calculate a due date from the Last Menstrual Period?

Add 280 days to the first day of your last period, or apply Naegele's Rule: add 7 days, then 9 months. Example: an LMP of January 1 gives January 8, then October 8. This assumes a 28-day cycle with ovulation on day 14. For a different cycle length, shift the date by the difference: \(\text{EDD} = \text{LMP} + 280 + (\text{cycle length} - 28)\) days. A 32-day cycle moves the EDD 4 days later, to October 12, and a 24-day cycle moves it 4 days earlier, to October 4.

What are the three trimesters of pregnancy and what happens in each?

ACOG sets the first trimester up to 13 weeks 6 days, the second from 14 weeks 0 days to 27 weeks 6 days, and the third from 28 weeks 0 days to birth. In the first trimester the main organs form, mostly in weeks 5 to 10, and most miscarriages occur. The second trimester is usually the most comfortable, with the anatomy scan around weeks 18 to 22 and movement felt from about weeks 16 to 25. In the third trimester the baby gains weight quickly and the lungs mature for birth.

What is a pregnancy due date calculator and how does it work?

A pregnancy due date calculator estimates your due date (EDD) from the first day of your last menstrual period (LMP), a conception date, or an IVF transfer date. From the LMP it adds 280 days (40 weeks), following Naegele's Rule, and then shows your current gestational week and trimester. Example: an LMP of January 1 gives an EDD of October 8. The result is a planning date for screenings and appointments, not a prediction of the day labor starts.

What is Naegele's Rule and is it still used today?

Naegele's Rule adds 7 days to the first day of your last period and then 9 months, which is the same as subtracting 3 months and adding 1 year. German obstetrician Franz Karl Naegele described it in the early 19th century, and clinics still use it as the quick LMP method. It matches the 280-day count only roughly. Months differ in length, so the two results differ by 0 to 3 days depending on the start date. For an LMP of January 1, 2028, Naegele gives October 8 and 280 days gives October 7. A first-trimester CRL measurement, accurate to about 5 to 7 days, confirms or adjusts either result.

What specific formulas does the pregnancy calculator use?

The calculator uses four counts. From the LMP: \(\text{EDD} = \text{LMP} + 280\) days. From a conception or ovulation date: \(\text{EDD} = \text{Conception} + 266\) days. From a 5-day blastocyst transfer: \(\text{EDD} = \text{Transfer} + 261\) days. From a 3-day embryo transfer: \(\text{EDD} = \text{Transfer} + 263\) days. The last two are 266 minus the embryo age at transfer. The tool adds days to the calendar date, so leap years and month lengths are handled.

Why is a conception date more precise for some pregnancies?

A known conception or ovulation date replaces the day-14 ovulation guess of the LMP method with a measured date. With irregular cycles, ovulation may fall on day 10 or day 20, which shifts an LMP-based EDD by the same number of days. If you track ovulation with basal body temperature or ovulation tests, enter that date and the calculator counts 266 days (38 weeks). Example: conception on May 15 gives an EDD of February 5 the next year.
Disclaimer: This calculator is designed to provide helpful estimates for informational purposes. While we strive for accuracy, financial (or medical) results can vary based on local laws and individual circumstances. We recommend consulting with a professional advisor for critical decisions.