Skip to main content

DigitalCalculators.net

Menu

Due Date Calculator

Estimate your baby’s due date from the first day of your last period, the conception date or an IVF transfer date, with weeks pregnant and trimester dates.

Results

ItemValue

Pregnancy timeline

MilestoneDate
This is an estimate. Only about 1 in 20 babies arrive on their due date. Your doctor or midwife may change the date after an early ultrasound. This tool is for information only and is not medical advice.

Quick Answer

Your due date is about 280 days, or 40 weeks, after the first day of your last period. This is called Naegele's rule. If your last period started on March 1, 2026, your estimated due date is Sunday, December 6, 2026. From a known conception date, add 266 days.

Last updated: 2 November 2026 ·How we calculate this: Naegele's rule and ACOG dating methods

Table of Contents

How This Due Date Calculator Works

Choose how you want to calculate: from the first day of your last menstrual period (LMP), from the conception date, or from an IVF embryo transfer. Enter the date, and for LMP, your usual cycle length. The calculator gives your estimated due date, how far along you are today, and the dates for each trimester and term stage.

Quick explanation: pregnancy is counted from the first day of your last period, about 2 weeks before conception.

  • Last period: add 280 days, adjusted for cycle length.
  • Conception: add 266 days.
  • IVF: add 263 days for a day 3 embryo or 261 days for a day 5 embryo.

How to Use the Due Date Calculator

  1. Choose last period, conception date or IVF transfer.
  2. Pick the date.
  3. For last period, enter your usual cycle length. 28 days is average.
  4. Press Calculate.
  5. Read your due date, how far along you are, and the timeline of trimesters.

Core Formulas

  • Naegele's rule: due date = LMP + 280 days
  • Cycle adjustment: add (cycle length − 28) days
  • From conception: due date = conception + 266 days
  • IVF day 3 transfer: due date = transfer + 263 days
  • IVF day 5 transfer: due date = transfer + 261 days

Key Terms

  • LMP: last menstrual period, counted from its first day.
  • Estimated due date (EDD): the date 40 weeks after the LMP.
  • Gestational age: how far along a pregnancy is, counted from the LMP.
  • Trimester: one of the three stages of pregnancy, each about 13 to 14 weeks.
  • Full term: 39 weeks 0 days to 40 weeks 6 days, the healthiest time for most births.

Worked Example

Your last period started on March 1, 2026, and your cycles are usually 32 days long.

  • March 1, 2026 + 280 days = Sunday, December 6, 2026
  • Cycle adjustment: 32 − 28 = 4 extra days
  • Estimated due date = Thursday, December 10, 2026

Real-Life Examples

  • A positive test: your last period started March 1, 2026, so your estimated due date is Sunday, December 6, 2026.
  • A known conception date: conception on February 14, 2026 gives a due date of Saturday, November 7, 2026.
  • IVF: a day 5 embryo transferred on April 10, 2026 gives a due date of Sunday, December 27, 2026.
  • Planning leave: use the 37-week and 39-week dates in the timeline to plan work and travel.

Gestational Age vs Fetal Age

  • Gestational age: counted from the first day of the last period. Doctors use this. A 40-week pregnancy is measured this way.
  • Fetal age: counted from conception, about 2 weeks less.
  • Example: at 10 weeks pregnant, the baby is about 8 weeks old since conception.

Pregnancy Stages by Week

Term definitions follow ACOG.

StageWeeks
First trimester0 to 13 weeks 6 days
Second trimester14 weeks to 27 weeks 6 days
Third trimester28 weeks to birth
Early term37 weeks to 38 weeks 6 days
Full term39 weeks to 40 weeks 6 days
Late term41 weeks to 41 weeks 6 days
Post-term42 weeks and later

Why Your Due Date Can Change

  • Early ultrasound: a first-trimester scan is the most accurate way to date a pregnancy, and may move your date.
  • Irregular cycles: ovulation timing is harder to know, so LMP dating is less certain.
  • Unsure LMP: if you do not remember the date, your provider will rely on ultrasound.
  • IVF: the transfer date gives a very exact due date.

Common Mistakes to Avoid

  • Using the last day of your period. Use the first day.
  • Counting from conception as LMP. Choose Conception date instead, or the date will be 2 weeks off.
  • Ignoring cycle length. Long or short cycles shift ovulation and the due date.
  • Expecting birth on the exact date. Most babies arrive within 2 weeks either side.
  • Skipping prenatal care. See a doctor or midwife to confirm your dates.

Frequently Asked Questions

Most often by adding 280 days (40 weeks) to the first day of the last menstrual period. This is called Naegele's rule.

It gives a good estimate. Only about 5% of babies are born on the exact date, and most arrive within 2 weeks of it.

Yes. An early ultrasound can change it if the baby's size does not match the date from your last period.

Count from the first day of your last period. This calculator shows weeks and days as of today.

LMP dating is less reliable. Enter your average cycle length, and ask about an early dating ultrasound.

Add 266 days, or 38 weeks, to the conception date.

Add 263 days to a day 3 embryo transfer date, or 261 days to a day 5 transfer date.

At 14 weeks 0 days.

At 28 weeks 0 days.

39 weeks 0 days to 40 weeks 6 days. 37 to 38 weeks is early term.

Doctors count from the last period because its date is usually known. Conception usually happens about 2 weeks later.

As soon as you think you are pregnant, contact a doctor or midwife to start prenatal care.

References & Sources

SourceUsed ForLink
ACOG Committee Opinion 700, Methods for Estimating the Due Date LMP, ultrasound and IVF dating. https://www.acog.org/clinical/guidance/committee-opinion/2017/05/methods-for-estimating-the-due-date
NHS, Due date calculator and pregnancy dating How due dates are estimated. https://www.nhs.uk/pregnancy/finding-out/due-date-calculator/