How accurate is the last menstrual period method?

The LMP method is an estimate based on average cycle length and assumes ovulation on day 14. For women with regular 28-day cycles, it's typically accurate to within a week. Women with irregular cycles or cycles longer/shorter than 28 days may find conception-date or ultrasound dating more accurate. Early ultrasound (8–13 weeks) is the clinical gold standard for dating.

What if my cycle isn't 28 days?

Longer cycles delay ovulation — a 35-day cycle typically means ovulation around day 21 rather than day 14, pushing the due date later by about 7 days. Shorter cycles advance ovulation. This calculator lets you adjust cycle length to account for this variation in the LMP calculation.

When does each trimester start?

First trimester: weeks 1–13 (conception through end of week 13). Second trimester: weeks 14–27. Third trimester: weeks 28–40+. These are approximate divisions used for clinical and planning purposes; exact week assignments vary slightly by source.

What does 'full term' mean?

Full term is defined as 39–40 weeks gestation. Early term is 37–38 weeks; late term is 41 weeks; post term is 42+ weeks. Babies born before 37 weeks are preterm. The 37–42 week window is considered the normal delivery range, though 39–40 weeks is associated with the best outcomes.

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When Is Your Baby Due? Estimate Your Due Date

When is your baby due?

What This Does

Your estimated due date (EDD) is one of the first and most important numbers in pregnancy — it sets the timeline for prenatal care, testing, and planning. The standard method of calculating an estimated due date is Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a regular 28-day cycle and ovulation on day 14, which is a population average that may not match your cycle precisely. If you know your conception date (or have a confirmed ovulation date), adding 266 days gives an equally reliable estimate. Early ultrasound dating — typically performed between 8 and 13 weeks — is considered the most accurate method and may adjust your due date by a few days based on fetal size. Only about 4% of babies are born exactly on their due date. Most full-term deliveries happen between 37 and 42 weeks. The due date is best understood as the center of a normal window, not a deadline. This calculator computes your estimated due date using both LMP and conception date methods, maps your current week of pregnancy, and shows key milestones: when each trimester begins, when prenatal screenings are typically scheduled, and when you'll enter the full-term window.

When Should You Use This?

→Estimating your due date from your last menstrual period
→Calculating how many weeks pregnant you are today
→Finding out when each trimester starts and ends
→Planning prenatal appointments and key screening dates
→Checking whether you're in the full-term (37–42 week) window

Example Scenario

Maya's last menstrual period started on October 15. Her due date using Naegele's rule: October 15 + 280 days = July 22. She is currently 14 weeks pregnant (entering the second trimester). Key dates: first trimester ended at week 13 (January 12), anatomy scan due around week 20 (March 5), full-term window begins at week 37 (June 18). The calculator maps all milestones on a visual timeline.

Pregnancy Due Date Calculator

EDD, Trimester Progress, Milestones & Baby Development

Enter your LMP or conception date — results update in real time.

Calculation Method

First Day of Last Period

Average Cycle Length (days)

Adjusts EDD for non-28-day cycles (range: 21–45 days)

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Enter your last period date above to calculate your due date and pregnancy timeline.

About This Calculator

This pregnancy due date calculator computes your estimated due date (EDD), current gestational age, trimester progress, and full pregnancy timeline in real time — updating instantly as you type. Two input methods are supported: Last Menstrual Period (LMP), which is the clinical standard, and Conception Date for those who know the exact date of conception (from IVF, IUI, or timed intercourse). Cycle length adjustment shifts the due date for non-28-day cycles using the standard ovulation offset formula.

The Timeline tab includes a stacked bar chart showing weeks completed in each trimester alongside remaining weeks, plus a comprehensive key dates summary from LMP through post-term. The Development tab renders a bar chart of all 14 development milestones from week 4 to week 40, with past milestones highlighted in your stage colour and a reference line at your current week — plus detailed emoji cards with size comparisons (poppy seed to watermelon) and developmental highlights.

The Milestones tab lists all 11 key prenatal appointments and screening tests (heartbeat detection, nuchal scan, anatomy scan, glucose screening, Group B Strep test, full term, EDD, post-term) with dates, week numbers, and days remaining. Dynamic accent colours shift with your pregnancy stage: blue (first trimester), green (second trimester), amber (third trimester), emerald (full term), and red (post-term). Export to PDF provides a print-ready document with all dates, the full milestone table, and baby development reference.