Pregnancy Due Date Calculator
Calculate your EDD using LMP, conception date, IVF transfer, or ultrasound measurements
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Quick summary
Your estimated due date (EDD) is 280 days (40 weeks) after the first day of your last menstrual period, a method called Naegele's rule. This calculator adjusts for cycles longer or shorter than 28 days, and can also work from a conception date, an IVF transfer date, or an ultrasound. A due date is an estimate: most babies arrive within a couple of weeks of it, and your doctor or midwife will confirm it.
Reviewed by Simple Calculators TeamLast reviewed
For information only — not medical advice. Results are estimates from published formulas and can't account for your health history. Talk to a doctor or other qualified clinician before making health decisions.
How to use this calculator
- Choose a Calculation Method: Last Menstrual Period (LMP), Known Conception Date, IVF Embryo Transfer Date, or Ultrasound Gestational Age.
- For LMP, enter the First Day of Last Period and your Average Cycle Length (days); leave it at 28 if you are unsure. Each day longer or shorter than 28 moves the due date by one day.
- For a known conception, enter the Conception Date. For IVF, enter the Transfer Date and the Embryo Age at Transfer (3-day or 5-day embryo).
- For an ultrasound, enter the Ultrasound Date and the gestational age from your scan report in Weeks at Ultrasound and Days.
- Click Calculate Due Date, then read your Estimated Due Date, how many weeks and days pregnant you are, days remaining, the trimester timeline, and key milestones. Confirm the date with your doctor or midwife.
Due Date Formulas
Naegele's Rule (Adjusted for Cycle Length)
- LMP
- First day of your last menstrual period
- C
- Average cycle length in days (28 if you leave the default)
- EDD
- Estimated due date (40 weeks of gestation)
Worked example
Last period started January 1, 2026; average cycle 28 days, and the same LMP with a 32-day cycle
- Given
- LMP = Jan 1, 2026C = 28 days (then 32 days)
- Calculation
- Result
- Due date: October 8, 2026 (28-day cycle) or October 12, 2026 (32-day cycle)
IVF Embryo Transfer Due Date
- Transfer Date
- The date the embryo was transferred
- d
- Days the transfer is treated as being past the equivalent LMP
Worked example
5-day (blastocyst) transfer on March 10, 2026
- Given
- Transfer Date = Mar 10, 2026d = 19
- Calculation
- Result
- Due date: November 26, 2026
Frequently asked questions
What is Naegele's Rule?
Naegele's rule estimates your due date by adding 280 days (40 weeks) to the first day of your last menstrual period. It assumes a 28-day cycle with ovulation around day 14. When you use the LMP method, this calculator adjusts for your cycle length, adding a day for each day your cycle is longer than 28 and subtracting a day for each day shorter.
How accurate is the due date calculator?
A due date is an estimate, and only a small share of babies arrive on the exact day. Births between 37 and 42 weeks are considered term. Early ultrasound, especially in the first trimester, is generally more accurate than period-based dating, particularly for people with irregular cycles or an uncertain LMP. Your doctor or midwife will confirm or adjust your due date.
How is an IVF due date calculated?
For IVF, the due date is counted from the transfer date, because the embryo's age is known precisely. A 5-day embryo transfer is treated as day 19 of an equivalent cycle (14 days to ovulation plus 5), so the due date is the transfer date plus 261 days. A 3-day transfer is treated as day 17, so the due date is the transfer date plus 263 days.
How is a due date calculated from an ultrasound?
The calculator subtracts the gestational age measured on your ultrasound from the scan date to find an equivalent LMP, then adds 280 days. For example, a scan showing 8 weeks and 2 days places the equivalent LMP 58 days before the scan. Dating from an early ultrasound is often preferred when it differs noticeably from period-based dating; your clinician decides which date to use.
How many weeks pregnant am I?
Pregnancy weeks are counted from the first day of your last menstrual period, not from conception, so you are considered about two weeks pregnant at conception. The calculator shows your current gestational age as weeks plus days (for example, 12+3) based on today's date and the method you chose. It also shows how many days remain until your estimated due date.
What are the three trimesters?
The first trimester runs through week 13, the second from week 14 through week 27, and the third from week 28 until birth. ACOG defines early term as 37–38 weeks, full term as 39–40 weeks, late term as 41 weeks, and post-term as 42 weeks or later; birth before 37 weeks is preterm. The calculator shows the dates each trimester starts and ends for your pregnancy.
Can my due date change?
Yes, your due date can change, most often after an early ultrasound. If the measured size of the embryo or fetus differs enough from your period-based date, your clinician may update your due date to match the scan. Once a reliable due date is set early in pregnancy, it is usually not changed later based on growth scans alone.
Can I use this if my cycles are irregular?
You can, but the result will be less reliable. Naegele's rule assumes predictable ovulation, so irregular or unknown cycles make LMP-based dates uncertain even with the cycle length adjustment. If you know your conception or IVF transfer date, or have had a dating ultrasound, choose that method instead. Ask your doctor or midwife about a dating scan if you are unsure.
Key terms
- Naegele's Rule
- The standard formula for estimating EDD: LMP + 280 days (40 weeks), assuming a 28-day cycle.
- EDD (Estimated Due Date)
- The projected delivery date, calculated as 40 weeks from the first day of the last menstrual period.
- Gestational Age
- The age of the pregnancy measured in weeks from the first day of the last menstrual period (LMP).
- Trimester
- One of three roughly 13-week periods that divide a pregnancy: first (weeks 1–13), second (14–27), third (28–40).
Methodology, sources & limitations
This page shows the formula, assumptions, and limitations used for this estimate. Rates, thresholds, and other time-sensitive inputs can change, so verify them against the relevant official source before relying on a result.
For our review approach and the primary sources we consult, see the methodology and source policy. If you spot an outdated figure or formula, please contact us with a correction.