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How Pregnancy Due Date & Milestone Calculator works
The Pregnancy Due Date & Milestone Calculator estimates your expected due date (EDD) and current gestational age using three clinically recognised methods: Naegele's Rule (from LMP), conception date calculation, and IVF embryo transfer dating. Each method is internationally recognised for establishing gestational age during prenatal care.
Naegele's Rule — the most widely used method — adds 280 days (40 weeks) to the first day of the last menstrual period, based on the assumption of a 28-day cycle with ovulation at Day 14. When an estimated conception date is supplied, 266 days (38 weeks from conception) are added instead. For IVF pregnancies, the transfer date plus 266 days minus the embryo age at transfer provides an embryo-age-adjusted estimate.
Beyond the due date, the calculator shows current gestational age in weeks and days, the current trimester with a visual progress bar, key pregnancy milestones (heartbeat detectable, anatomy scan window, viability, third trimester onset), and a fun baby size comparison widget.
How to use Pregnancy Due Date & Milestone Calculator
1. Select your dating method
Choose from three tabs: "By Last Period" for Naegele's Rule, "By Conception Date" if you know when conception occurred, or "By IVF Transfer" for IVF pregnancies with known embryo age at transfer.
2. Enter the relevant date
Input the date corresponding to your selected method: LMP date, estimated conception date, or embryo transfer date along with embryo age at transfer (Day 3 or Day 5).
3. View your due date and gestational age
The calculator immediately displays your estimated due date, a live countdown, your current gestational age in weeks and days, and your current trimester.
4. Explore milestones and baby size
Scroll through the milestone timeline to see when key prenatal events occur, and check the baby size comparison widget that shows your baby's approximate size as a familiar fruit or vegetable.
Key features and technical specifications
Naegele's Rule & Three Dating Methods
Supports LMP-based Naegele's Rule (LMP + 280 days), conception-date calculation (+ 266 days), and IVF transfer dating with embryo age adjustment.
Current Gestational Age Display
Shows precise gestational age in weeks and days, updated in real time based on today's date.
Trimester Progress Bar
Visual three-stage progress bar clearly indicates which trimester (1st, 2nd, or 3rd) the current gestational age falls within.
Baby Size Comparison Widget
Week-by-week fruit and vegetable size comparisons (e.g., "Size of a lemon at Week 14") make gestational progression tangible and engaging.
Pregnancy Milestone Timeline
Annotated timeline of key prenatal milestones including heartbeat detection, first-trimester screening, anatomy scan, viability threshold, and term dates.
A due date is an estimate for care planning
Gestational age and time since conception use different starting points. Record which method you selected when sharing a result, particularly for embryo transfers. Your maternity team may revise dates using clinical information and ultrasound. A countdown does not predict the day labor will start, and milestone dates are not a substitute for prenatal appointments.
Newly pregnant — establishing a due date
Calculate your EDD immediately after a positive pregnancy test before your first prenatal appointment, using Naegele's Rule.
IVF pregnancies
For monitored IVF cycles, calculate the most accurate due date using the embryo transfer date and Day-3 or Day-5 embryo age at transfer.
Sharing pregnancy news
Confirm gestational age and trimester for sharing pregnancy announcements or discussing your stage of pregnancy with family and care providers.
Frequently asked questions
What is Naegele's Rule?
Naegele's Rule is the standard obstetric formula for estimating the due date from the last menstrual period. It adds 280 days (40 weeks) to the LMP date, based on the assumption of a 28-day cycle with ovulation at Day 14. The formula is named after German obstetrician Franz Karl Naegele and has been in clinical use since the 19th century.
How accurate is the calculated due date?
Only about 5% of babies are born on their exact due date. The EDD represents the midpoint of a normal delivery range spanning roughly 37–42 weeks of gestation. First-trimester ultrasound measurements of the fetal crown-rump length (CRL) are generally considered more accurate than LMP-based dating and may revise your EDD.
What is gestational age vs. fetal age?
Gestational age counts from the first day of the LMP — approximately 2 weeks before fertilisation — and is the standard clinical dating convention used by obstetricians. Fetal age (or embryonic age) counts from the actual date of fertilisation and is approximately 2 weeks less than gestational age. All weeks referenced by OB-GYNs and ultrasounds use gestational age.
What is the difference between the three dating methods?
The LMP method (Naegele's Rule) assumes a standard 28-day cycle and is appropriate when the exact conception date is unknown. The conception date method is more accurate when ovulation timing was confirmed (via OPK or temperature charting). The IVF transfer method is most precise for assisted reproduction, using the known transfer date and embryo developmental stage to calculate backward to a standardised gestational age baseline.
When do the trimesters start and end?
The first trimester runs from conception through the end of Week 13 (Weeks 1–13). The second trimester spans Weeks 14–26. The third trimester covers Weeks 27 through delivery. Some classifications use slightly different boundaries; these are the most widely accepted obstetric definitions.
Do I need an internet connection, and are my inputs uploaded?
An internet connection is required to open tools and refresh a temporary session. Processing stays on your device; the handshake sends a random challenge, not files or text inputs. Libraries, fonts or models may download. Local processing cannot remove risks from an untrusted device or extension.
Further reading
These references explain the topic and its limitations. They do not endorse or clinically validate this calculator.