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Pregnancy Due Date Calculator

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Calculate your pregnancy due date from your last menstrual period (LMP). Know your gestational age, trimester, and days remaining using Naegele's rule.

Reviewed by the thecalcu.com team · Last updated June 28, 2026

June 23rd, 2026

Enter the first day of your last period

Average Cycle Length
days
20 days45 days

Estimated Due Date

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Trimester

1st

Weeks Pregnant

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Days Until Due

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Select your LMP date above

What is a Pregnancy Due Date?

A pregnancy due date calculator estimates when your baby is expected to arrive, the Estimated Due Date (EDD), based on the first day of your Last Menstrual Period (LMP). This uses Naegele's rule, the standard obstetric dating method: due date = LMP + 280 + (your cycle length − 28) days. For a standard 28-day cycle, that simplifies to LMP + 280 days, or 40 weeks.

This calculator is for general educational reference only and is not medical advice. It does not replace an ultrasound-confirmed due date or the judgment of a licensed OB-GYN or midwife, and it cannot account for individual pregnancy history or complications. Always confirm your due date and prenatal care schedule with a healthcare provider, most will confirm or adjust the estimate using a first-trimester ultrasound.

Along with the due date, the calculator returns your current gestational age in weeks, days pregnant, days remaining until your due date, and your current trimester. Pair it with the Ovulation Calculator for cycle and conception planning, or the Period Calculator for general cycle tracking.

How to use this Pregnancy Due Date calculator

  1. Enter the first day of your last menstrual period (LMP) in the date field. If you're unsure, use the date your last period started.
  2. Enter your average cycle length using the slider. The default is 28 days, adjust it if your cycles typically run longer or shorter.
  3. Read the result: days until your due date (highlighted), weeks pregnant, days pregnant, and current trimester.
  4. To find the calendar due date itself, add "Days Until Due Date" to today's date, or check the steps panel, which displays the full EDD.
  5. Use the trimester figure to get a general sense of which prenatal milestones and tests are typically relevant at your stage.
  6. Bring the estimate to your first prenatal visit, your provider will confirm or refine it using ultrasound measurements.

What Insights Does This Calculator Give You?

Days Until Due Date is the primary, highlighted output, a practical countdown useful for planning parental leave, packing a hospital bag, or simply knowing roughly how much time remains.

Weeks Pregnant (Today) and Days Pregnant (Today) give your current gestational age, the figure your provider uses to track fetal development milestones and time routine screening tests.

Current Trimester tells you which of the three broad phases of pregnancy you're in, useful shorthand for understanding what kind of appointments and tests are typically scheduled around this stage, though your provider's exact schedule may vary.

None of these outputs are a diagnosis or a guarantee, they're standard-formula estimates meant to sit alongside, not replace, your provider's ultrasound-based dating and ongoing prenatal care.

Common Mistakes to Avoid

Entering the wrong reference date. LMP means the first day of your last period started, not the last day it ended or the date you suspect conception occurred, mixing these up shifts every downstream figure by days or weeks.

Assuming a 28-day cycle when yours runs differently. Skipping the cycle-length adjustment on a consistently longer or shorter cycle introduces an error that compounds over the following calculations, take the extra step to enter your actual average.

Treating the EDD as a fixed delivery date. Only about 4% of babies arrive on their exact due date. Treat the result as the center of a roughly four-week window, not a firm appointment.

Skipping the ultrasound confirmation. LMP-based dating is a starting estimate, not a final answer, especially for irregular cycles, recent hormonal contraceptive use, or uncertain LMP recall, where an early ultrasound is meaningfully more accurate.

Delaying a first prenatal visit until the due date feels "confirmed." The due date calculation itself isn't a prerequisite for starting care, schedule your first appointment as soon as you suspect pregnancy, and let your provider handle dating from there.

Quick Reference

Trimester Weeks (from LMP) Days (from LMP)
First 1–13 1–91
Second 14–26 92–182
Third 27–40 183–280
Term category Week range
Preterm Before 37
Early term 37–38
Full term 39–40
Late term 41
Post-term 42+

Related tools: the Ovulation Calculator for cycle and conception timing, the Gestational Age Calculator for a more detailed age breakdown, and the Reverse Due Date Calculator if you want to work backward from a target due date to an implied LMP.

Formula & Methodology

Naegele's Rule (adjusted for cycle length):

EDD = LMP + 280 + (cycle_length − 28) days

For a standard 28-day cycle: EDD = LMP + 280 days = LMP + 40 weeks.

Trimester boundaries (from LMP):
- Trimester 1: Days 1–91 (Weeks 1–13)
- Trimester 2: Days 92–182 (Weeks 14–26)
- Trimester 3: Days 183–280 (Weeks 27–40)

Worked example, LMP January 1, cycle length 30 days:

Gestation period = 280 + (30 − 28) = 282 days EDD = Jan 1 + 282 days = October 9 If today is April 1:   Days pregnant  = 90 days → end of Trimester 1   Weeks pregnant = 12 weeks, 6 days   Days until due = 191 days

Assumptions and limitations: this calculation assumes a known, accurate LMP date and a regular cycle length. It doesn't account for irregular ovulation timing, assisted reproduction (IVF) protocols with a known transfer date, or individual variation in gestation length, a licensed provider's ultrasound-based dating should always take precedence over this estimate.

Frequently Asked Questions

This calculator uses Naegele's rule: add 280 days (40 weeks) to the first day of your Last Menstrual Period (LMP). If your cycle isn't 28 days, it adjusts: due date = LMP + 280 + (your cycle length − 28) days. A 30-day cycle, for example, gives LMP + 282 days. This is an estimate, not a guarantee, your doctor may adjust it based on an ultrasound.
LMP stands for Last Menstrual Period, the first day of your most recent period before pregnancy began. Conception typically happens around day 14 of a 28-day cycle (ovulation), but the exact conception date is genuinely hard to pin down. LMP is easy to recall and gives a consistent, known reference point, which is why it's the standard starting point for gestational age calculations in clinical practice.
Gestational age in weeks counts from the LMP date, not the conception date. So when a provider says you're '8 weeks pregnant,' that includes roughly 2 weeks before conception actually occurred. A full-term pregnancy runs 40 weeks (280 days) from LMP. Babies born between 37 and 42 weeks are considered full-term; before 37 weeks is preterm.
Pregnancy is divided into three trimesters, each roughly 13 weeks. First trimester: weeks 1–13 (LMP day 1 to day 91), major organ development and the highest miscarriage risk window. Second trimester: weeks 14–26 (days 92–182), often the most comfortable phase, with fetal movement beginning. Third trimester: weeks 27–40 (days 183–280), rapid growth and preparation for birth.
It's an estimate, only about 4% of babies are born on their exact due date. Roughly 80% of births happen within 2 weeks before or after the EDD, between weeks 38 and 42. A first-trimester ultrasound (crown-rump length measurement) is generally more accurate than LMP-based calculation, especially if your LMP is uncertain or your cycles are irregular. Your provider will use ultrasound to confirm or adjust the estimate at your first prenatal visit.
Ovulation typically occurs about 14 days before your next period starts, not 14 days after LMP, so for a 30-day cycle, ovulation lands closer to day 16, and conception happens roughly 2 days later than it would in a standard 28-day cycle. This calculator accounts for that: due date = LMP + 280 + (cycle length − 28) days. Enter your actual average cycle length for a closer estimate; for very irregular cycles, ultrasound dating is the more reliable option.
All three describe the same thing. EDD means Estimated Due Date, the most commonly used term. EDB means Estimated Date of Birth. EDC means Estimated Date of Confinement, an older term still seen on some clinical records. Whichever term your provider uses, it refers to the same calculated date this tool produces.
Many health guidelines recommend scheduling a first prenatal visit within the first 8–12 weeks of pregnancy. Your provider will typically confirm your due date with an early ultrasound and outline a schedule of visits and screening tests from there. If you think you might be pregnant, don't wait for a due date calculation to schedule that first appointment.
If you're not sure of your LMP, your provider can use a first-trimester ultrasound (crown-rump length measurement) to estimate gestational age instead. This method is accurate to within about ±5–7 days in the first trimester and ±2 weeks in the second. For anyone with irregular cycles, PCOS, or recent use of hormonal contraception, ultrasound dating is generally the preferred approach.
Early term is 37–38 weeks, full term is 39–40 weeks, late term is 41 weeks, and post-term is 42 weeks or beyond, all measured from LMP. Preterm birth, before 37 weeks, carries higher risks of complications for the newborn, which is part of why accurate dating and consistent prenatal care matter.
Yes, add 266 days (38 weeks) to a known or estimated conception date to get the EDD. If you know the date of intercourse that led to conception, the actual conception date is typically 0–5 days later, since sperm can survive up to 5 days in the reproductive tract. Exact conception dates are rarely known with certainty, though, which is why LMP-based calculation remains the clinical standard, use this calculator with your LMP date as the input.
No. This tool gives a general educational estimate based on standard obstetric dating rules, not a medical diagnosis or a guarantee of your actual delivery date. It cannot account for individual health conditions, prior pregnancy history, or ultrasound findings. Always confirm your due date and pregnancy progress with a licensed OB-GYN or midwife.
Also known as
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