Due Date Calculator — Pregnancy Due Date from LMP, Conception, or IVF
📜 ACOG source for due-date estimation
The estimated due date uses Naegele’s rule (LMP + 280 days), the standard cited by ACOG. Only about 4–5% of births occur on the EDD itself; the clinically normal window is 37–42 weeks. Ultrasound dating in the first trimester supersedes LMP-based estimates when they differ. Last reviewed: June 2026.
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How is the pregnancy due date calculated?
From LMP (Last Menstrual Period): Due date = LMP + 280 days. Assumes 28-day cycle with ovulation on Day 14. Adjust for longer or shorter cycles: Due date = LMP + 280 − (28 − cycle length). Related: use the Pregnancy Calculator to go further, or the Ovulation Calculator for a different angle.
From conception date: Due date = Conception date + 266 days (38 weeks from fertilisation).
From IVF transfer: Day-5 (blastocyst) transfer: Due date = Transfer date + 266 days. Day-3 transfer: Due date = Transfer date + 268 days.
Pregnancy week-by-week milestones
| Week | Trimester | Milestone |
|---|---|---|
| 4–6 | First | Home pregnancy test positive; embryo implanting |
| 6–8 | First | Heartbeat detectable on transvaginal ultrasound |
| 8–10 | First | First prenatal appointment; NIPT/CVS if requested |
| 11–14 | First | First trimester screening; nuchal translucency scan |
| 13 | First ends | Miscarriage risk drops significantly |
| 16–18 | Second | Gender potentially visible; quadruple screen blood test |
| 18–22 | Second | Anatomy scan (anomaly ultrasound) |
| 20 | Second | Halfway point; most women feel their best |
| 24–28 | Second | Glucose tolerance test; baby is viable if born early |
| 28 | Third begins | Fetal movement counting; Group B Strep test later |
| 36 | Third | Baby considered early term; GBS swab; weekly appointments begin |
| 37–40 | Full term | Birth expected any time; normal delivery window |
| 40+ | Post-term | Induction discussed if no labour by 41–42 weeks |
How accurate is the due date?
Naegele's Rule (LMP method) is accurate to within 2 weeks for women with regular 28-day cycles. For irregular cycles, first trimester ultrasound (8–12 weeks) is more accurate — it can estimate gestational age within 5–7 days. After 20 weeks, ultrasound accuracy decreases to ±3 weeks. Only 4–5% of babies are born on their exact due date; about 70% arrive within 10 days.
Health disclaimer: This calculator provides estimates for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Results are based on population averages and may not apply to individuals with specific health conditions. Always consult a qualified healthcare professional. Reviewed by Dr. P Nair, MBBS, MD.
Frequently asked questions
How do you calculate a due date from LMP?
Add 280 days (40 weeks) to the first day of your last menstrual period. Example: LMP = January 1, 2026. Due date = January 1 + 280 days = October 8, 2026. For cycle length other than 28 days: adjust by (cycle length − 28) days. 35-day cycle: add 7 more days to the LMP calculation.
What is gestational age vs fetal age?
Gestational age counts from the first day of the LMP — the standard medical measurement. Fetal (conceptional) age counts from conception — typically 2 weeks less than gestational age. When a doctor says 'you are 8 weeks pregnant,' they mean 8 weeks gestational age. The baby has been developing for approximately 6 weeks since fertilisation.
When should I see a doctor after a positive pregnancy test?
Schedule your first prenatal appointment for 8–10 weeks gestational age. If you have a history of miscarriage, are over 35, have chronic conditions (diabetes, thyroid disease, hypertension), or conceived via IVF, request an earlier appointment at 6–7 weeks for an early reassurance scan.
What is a full-term pregnancy?
ACOG defines term pregnancies as: Early term 37 0/7 – 38 6/7 weeks, Full term 39 0/7 – 40 6/7 weeks, Late term 41 0/7 – 41 6/7 weeks, Post-term 42 weeks or beyond. Outcomes are best for deliveries at 39–40 weeks. Planned deliveries before 39 weeks are avoided unless medically necessary.
How is the due date different for twins?
Twin pregnancies are measured the same way (LMP + 280 days) but the expected delivery is earlier: dichorionic-diamniotic twins (DCDA): planned delivery at 38 weeks. Monochorionic-diamniotic (MCDA): 36–37 weeks. Monochorionic-monoamniotic (MCMA): 32–34 weeks. Use the standard due date calculator then discuss timing with your obstetrician.
Sources & References
Sources: ACOG Practice Bulletin No. 700 — Methods for Estimating the Due Date (2022); Naegele, F.C. (1812) — original LMP rule publication; WHO Recommendations on Antenatal Care (2016); NHS Pregnancy care guidelines.
What happens each trimester of pregnancy?
First trimester: weeks 1–13
The first trimester is the most critical for fetal development — all major organs form during this period. Weeks 4–6: home pregnancy test positive; embryo size of a poppy seed; implantation complete. Weeks 6–8: heartbeat detectable on transvaginal ultrasound; embryo size of a lentil. Weeks 8–10: first prenatal appointment; embryo becomes a fetus at week 9; all essential organs forming. Weeks 11–14: nuchal translucency scan; chromosomal screening (NIPT, CVS available); risk of miscarriage drops significantly after week 12.
Common first trimester symptoms: nausea (morning sickness), extreme fatigue, breast tenderness, frequent urination, food aversions, heightened smell sensitivity. About 70–80% of pregnant women experience nausea; it typically peaks around week 9 and resolves by week 14 for most.
Second trimester: weeks 14–27
Most women feel their best during the second trimester — morning sickness eases, energy returns, and the pregnancy becomes visible. Weeks 16–18: anatomy can often be seen on ultrasound; quadruple screen blood test. Weeks 18–22: anatomy scan (anomaly scan) — the most detailed ultrasound of the pregnancy, checking all major organs and structures. Week 20: halfway point. Weeks 24–28: glucose tolerance test for gestational diabetes; baby reaches viability (survival outside womb with medical support) by week 24.
Third trimester: weeks 28–40+
Weeks 28–36: fetal movement counting becomes important; growth scans if needed; baby gains weight rapidly. Week 36: Group B Streptococcus (GBS) swab. Week 37: baby is considered early term. Weeks 39–40: full term — the safest window for delivery. Weeks 41–42: post-term; induction discussed with OB. Signs of labour: regular contractions (every 5 minutes for 1 hour), water breaking, bloody show. Go to hospital immediately if: water breaks with coloured/smelly fluid, no fetal movement for 12 hours, heavy vaginal bleeding, severe headache with visual disturbance.
Antenatal appointment schedule in India (ICMR guidelines)
| Visit | Gestational Week | What Happens |
|---|---|---|
| Registration / Booking | 8–12 weeks | Complete blood panel, blood group, HIV, hepatitis, urine test, blood pressure baseline, weight |
| First visit | 14–16 weeks | Blood pressure, weight, fundal height, fetal heart rate |
| Anatomy scan | 18–20 weeks | Detailed anomaly ultrasound |
| Second visit | 24–28 weeks | Glucose tolerance test, blood pressure, weight, fundal height |
| Third visit | 32 weeks | Fetal presentation, blood pressure, anaemia screen |
| Fourth visit | 36 weeks | Fetal position (cephalic/breech), birth plan discussion |
| Weekly visits | 37–40 weeks | Fetal monitoring, cervical assessment |
Source: ICMR-NIN Antenatal Care Guidelines; Ministry of Health and Family Welfare, Government of India.
Related: Pregnancy Calculator for gestational age · Ovulation Calculator for conception planning.
Our formulas and sources: Calculation Methodology · Editorial Policy
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⚕️ Medical disclaimer: This calculator provides educational estimates only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. Formulas and reference ranges follow WHO and ICMR published guidelines — see our methodology.