Pregnancy Due Date Calculator — EDD & Milestones
Calculate your estimated due date from LMP, conception date, IVF transfer date, or ultrasound. Get week-by-week milestones, trimester dates, and key prenatal appointment windows.
Calculation Method
What Is the Pregnancy Due Date Calculator — EDD & Milestones?
This calculator estimates your Estimated Due Date (EDD) using four clinically recognised methods: last menstrual period (LMP), conception date, IVF embryo transfer date, and ultrasound dating. It also calculates your current gestational age, trimester boundaries, key prenatal milestones, days remaining until your due date, and a traditional Chinese lunar gender prediction (clearly labelled as folklore, not medicine).
- ›Four input modes — LMP (most common), conception date, IVF Day 3 or Day 5 transfer, or an existing ultrasound with gestational age.
- ›Gestational age — calculated from the LMP-derived EDD and today's date, updated in real time.
- ›Trimester dates — exact calendar dates for the start of each trimester based on your EDD.
- ›Key milestone table — 13 clinically important dates from heartbeat detection at 6 weeks through the full-term milestone at 37 weeks.
- ›Countdown — days and weeks remaining until EDD, updated from today.
- ›Cycle-length adjustment — for LMP mode, the calculator adjusts for cycles longer or shorter than the standard 28 days.
Formula
From Last Menstrual Period (Naegele's Rule)
EDD = LMP + 280 days
EDD = LMP + (cycle length − 28) days + 280 days
From Conception Date
EDD = Conception Date + 266 days (38 weeks)
From IVF Transfer Date
EDD = Transfer Date + 266 days (Day 5 blastocyst)
EDD = Transfer Date + 268 days (Day 3 embryo)
From Ultrasound (Dating Scan)
EDD = Ultrasound Date + (280 − gestational_age_days)
| Term | Full Name | Description |
|---|---|---|
| LMP | Last Menstrual Period | First day of the last menstrual period before conception |
| EDD | Estimated Due Date | The projected date of birth — 40 weeks from LMP on average |
| GA | Gestational Age | Age of pregnancy from LMP, measured in weeks and days |
| T1 | First Trimester | Weeks 1–13 (0–13w6d from LMP) |
| T2 | Second Trimester | Weeks 14–27 (14w0d–27w6d from LMP) |
| T3 | Third Trimester | Weeks 28–40 (28w0d onward) |
| NIPT | Non-Invasive Prenatal Test | Blood test for chromosomal conditions; typically done at 10–13 weeks |
| NT | Nuchal Translucency Scan | Ultrasound scan for Down syndrome markers; done at 11–14 weeks |
How to Use
- 1Select input mode: Choose from Last Menstrual Period, Conception Date, IVF Transfer, or Ultrasound.
- 2Enter your date: Pick the relevant date using the date picker. For LMP, also adjust cycle length if it differs from 28 days.
- 3For IVF: Select whether your transfer was a Day 3 embryo or Day 5 blastocyst — this changes the EDD by 2 days.
- 4For ultrasound: Enter the date the scan was performed and the gestational age (weeks + days) measured at that scan.
- 5Press Calculate: Your EDD, gestational age, trimester dates, milestone table, and countdown appear instantly.
- 6Review milestones: Use the milestone table to track upcoming prenatal appointments and key developmental markers.
- 7Consult your provider: Your healthcare provider may adjust the EDD based on clinical examination and ultrasound findings.
Example Calculation
LMP = January 15, 2026 — cycle length 28 days
Input: LMP = Jan 15 2026, Cycle = 28 days
Step 1: Standard EDD = LMP + 280 days
Jan 15 + 280 days = October 22, 2026
Step 2: Cycle adjustment = 28 − 28 = 0 days
EDD = October 22, 2026
Step 3: If today is April 21, 2026 →
GA = (Apr 21 − Jan 15) = 96 days = 13w 5d
Trimester: First (ends week 13+6)
Days remaining: Oct 22 − Apr 21 = 184 days
| Milestone | Week | Date (approx.) |
|---|---|---|
| First heartbeat detectable | 6w | Feb 26, 2026 |
| Embryo → fetus transition | 8w | Mar 12, 2026 |
| NIPT window opens | 10w | Mar 26, 2026 |
| NT scan window | 12w | Apr 9, 2026 |
| Second trimester begins | 14w | Apr 23, 2026 |
| Anatomy ultrasound | 20w | Jun 4, 2026 |
| Viability milestone | 24w | Jul 2, 2026 |
| Third trimester begins | 28w | Jul 30, 2026 |
| Full term | 37w | Sep 17, 2026 |
| EDD | 40w | Oct 22, 2026 |
Understanding Pregnancy Due Date — EDD & Milestones
Medical Disclaimer
This calculator provides general health and fitness information for educational purposes. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any health decisions about your pregnancy.
How Is the Due Date Calculated?
The most widely used method is Naegele's Rule, developed in the 19th century: add 280 days (40 weeks) to the first day of the last menstrual period. This assumes a 28-day cycle with ovulation on day 14. For cycles that differ, the EDD is adjusted by the number of days the cycle deviates from 28. A 32-day cycle shifts the EDD forward by 4 days; a 24-day cycle moves it back by 4 days.
Ultrasound dating in the first trimester (before 14 weeks) is considered more accurate than LMP dating because it directly measures the embryo's crown-rump length. Your provider may "re-date" your pregnancy if the ultrasound EDD differs from the LMP EDD by more than 5–7 days.
The Three Trimesters
- ›First trimester (weeks 1–13): Rapid organ formation. Most miscarriages occur here. Key tests: NIPT (10–13 weeks), NT scan (11–14 weeks), first prenatal blood panel.
- ›Second trimester (weeks 14–27): The "comfortable" trimester for many. Anatomy ultrasound at 18–20 weeks. Glucose screening at 24–28 weeks. Movement (quickening) felt at 16–22 weeks.
- ›Third trimester (weeks 28–40+): Rapid fetal weight gain. GBS test at 35–37 weeks. Fetus considered "full term" at 37 weeks, "early term" 37–38w, "full term" 39–40w, "late term" 41w, "post-term" ≥42 weeks.
IVF Dating: Day 3 vs. Day 5 Transfer
In IVF pregnancies, the EDD is calculated differently because the date of fertilisation is precisely known. For a Day 5 blastocyst transfer, the EDD is 266 days after transfer (equivalent to 38 weeks of embryonic age). For a Day 3 embryo transfer, the EDD is 268 days after transfer. This is because a Day 3 embryo is 2 days younger than a Day 5 blastocyst at the time of transfer — it needs 2 extra days to reach the equivalent stage.
Only 5% of Babies Are Born on Their Due Date
The EDD is a statistical estimate, not a prediction. Research consistently shows that only about 4–5% of babies arrive on their exact due date. About 80% are born within two weeks either side of the EDD. Factors that influence the actual birth date include maternal age, parity (number of previous pregnancies), fetal sex, and genetics. First-time mothers tend to deliver slightly later than the EDD on average.
Related tools
Also see our Ovulation Calculator for fertile window prediction, and the Age Calculator for date arithmetic.
What Is Gestational Age vs. Fetal Age?
Gestational age is counted from the LMP — the standard used by clinicians worldwide. At the moment of conception (usually around day 14 of the cycle), the pregnancy is already "2 weeks old" by gestational age. Fetal age(also called embryonic age or conceptional age) is counted from fertilisation — it is always approximately 2 weeks less than gestational age. When your provider says "you are 10 weeks pregnant," they mean 10 weeks gestational age; the embryo itself is about 8 weeks old.
Frequently Asked Questions
How accurate is the estimated due date?
The EDD is an estimate, not a guarantee. Key accuracy considerations:
- ›LMP-based dating is accurate to ±2 weeks in the absence of cycle irregularity.
- ›First-trimester ultrasound is accurate to ±5 days — the most reliable method.
- ›Second-trimester ultrasound is accurate to ±2 weeks.
- ›Only ~5% of babies arrive on the exact EDD; ~80% are born within 2 weeks either side.
What is the difference between LMP and conception date methods?
Both methods calculate the same EDD for a 28-day cycle:
- ›LMP + 280 days = EDD (includes the 2 weeks before ovulation)
- ›Conception Date + 266 days = EDD (starts from fertilisation)
- ›The two are equivalent: 280 − 14 days of pre-ovulation = 266 days
- ›If your cycle is longer than 28 days, ovulation happens later, shifting the EDD forward.
How does IVF due date calculation differ from natural conception?
- ›Day 5 blastocyst: EDD = transfer date + 266 days (38 weeks post-fertilisation)
- ›Day 3 embryo: EDD = transfer date + 268 days (the embryo is 2 days younger)
- ›Frozen embryo transfer (FET) uses the same formula as fresh transfer
- ›IVF dating is often considered the most precise because fertilisation date is exact
What does "full term" mean and when can the baby safely arrive?
- ›Preterm: before 37 weeks
- ›Early term: 37w0d – 38w6d
- ›Full term: 39w0d – 40w6d (optimal birth window)
- ›Late term: 41w0d – 41w6d
- ›Post-term: 42 weeks or more (increased risk of complications)
Most providers consider induction at 41–42 weeks due to declining placental function.
When should I get my first prenatal appointment?
- ›6–8 weeks: Viability ultrasound (optional but reassuring)
- ›8–10 weeks: First prenatal appointment — blood work, history, risk assessment
- ›10–13 weeks: NIPT blood test (chromosomal screening)
- ›11–14 weeks: Nuchal translucency ultrasound (NT scan)
- ›18–20 weeks: Anatomy (anomaly) scan — gender may be revealed
- ›24–28 weeks: Glucose tolerance test (gestational diabetes screening)
- ›35–37 weeks: Group B Strep (GBS) test
What is the Chinese gender prediction calendar, and is it accurate?
The Chinese gender prediction calendar is a folk tradition, not medicine:
- ›Based on the mother's lunar age and the lunar month of conception
- ›No peer-reviewed evidence supports its accuracy beyond 50% (random chance)
- ›Multiple scientific studies have found it no better than a coin flip
- ›Actual sex can be determined by NIPT (10+ weeks) or anatomy scan (18–20 weeks)
What is the conception window and when does it show?
The conception window is displayed in LMP mode:
- ›Ovulation estimated as: LMP + (cycle length − 14)
- ›Conception window: 5 days before ovulation through 1 day after
- ›Peak fertility: 1–2 days before and on ovulation day
- ›Sperm can survive up to 5 days; the egg survives 12–24 hours after ovulation
For a detailed fertile window breakdown, use the Ovulation Calculator.
Can I use this calculator if my cycles are irregular?
- ›The cycle length field (21–45 days) adjusts the EDD for non-28-day cycles
- ›For irregular cycles, enter your best average cycle length as an approximation
- ›First-trimester ultrasound before 12 weeks is the gold standard for dating in irregular cycles
- ›PCOS, recent hormonal contraceptive use, or breastfeeding can cause irregular cycles that affect accuracy