Pregnancy Due Date Calculator — When Is My Baby Due?
Calculate when your baby is due from your last period (LMP), conception date, or IUI date. See your trimester timeline instantly.
Reviewed by Dr. Rukkayal Fathima, MRCOG (UK)
How Is Your Due Date Calculated?
The most common method 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 where ovulation happens around day 14.
If you know your conception date or had an IUI procedure, the calculation is slightly different — 266 days (38 weeks) from that date, since it skips the pre-ovulation phase.
Keep in mind that due dates are estimates. Only about 5% of babies arrive on the exact predicted date. Most are born within a 2-week window around the estimated due date. Your doctor may refine the estimate with an early ultrasound, especially if your cycles are irregular or longer than 28 days.
Your Pregnancy Trimester Guide
First Trimester (Weeks 1–12): This is when your baby's major organs begin to form — the heart starts beating by week 6. You may experience morning sickness, fatigue, and breast tenderness. Your first prenatal visit should happen during this trimester, ideally within the first 8 weeks.
Second Trimester (Weeks 13–27): Often called the "golden trimester" as nausea usually subsides. Around week 20, you will have a detailed anatomy scan to check your baby's development. You may start feeling your baby's movements (quickening) between weeks 16–22.
Third Trimester (Weeks 28–40): Your baby gains weight rapidly and the lungs mature. Prenatal visits become more frequent — usually every 2 weeks, then weekly from week 36. You and your doctor will discuss delivery planning, including signs of labour and when to go to the hospital.
Prenatal Check-Up Schedule
- Week 6–8: First prenatal visit — confirm pregnancy, blood tests, dating scan
- Week 11–13: NT scan (nuchal translucency) — screens for chromosomal conditions
- Week 18–22: Anomaly scan — detailed ultrasound to check baby's organs and growth
- Week 24–28: Glucose tolerance test — screens for gestational diabetes
- Week 28–36: Fortnightly visits — monitor blood pressure, baby's position, growth
- Week 36–40: Weekly visits — assess readiness for delivery, discuss birth plan
Starting prenatal care early gives you and your baby the best chance for a healthy pregnancy. If you have conceived through IVF, IUI, or have a high-risk pregnancy, your doctor may recommend additional monitoring.
Expert Care for Your Pregnancy
Frequently Asked Questions
Due date calculators based on Naegele's rule (LMP + 280 days) are accurate for women with regular 28-day cycles. However, only about 5% of babies arrive on their exact due date. Most are born within 2 weeks of the estimated date. An early ultrasound can refine the estimate.
Naegele's rule is the standard method used by doctors worldwide: add 280 days (40 weeks) to the first day of your last menstrual period. It assumes a 28-day cycle with ovulation on day 14.
Yes. If you know your conception date, add 266 days (38 weeks). This is because there are approximately 14 days between the start of your last period and conception.
Yes. If your cycles are longer than 28 days, you likely ovulated later, which pushes your due date forward. Your doctor may adjust the due date based on an early ultrasound measurement.
Schedule your first prenatal visit within the first 8 weeks. Early monitoring is important for confirming the pregnancy location, checking the heartbeat, and establishing accurate dating.
First trimester: weeks 1-12 (organ formation, highest miscarriage risk). Second trimester: weeks 13-27 (anatomy scan, baby movements). Third trimester: weeks 28-40 (rapid growth, preparation for delivery).
For IUI pregnancies, the due date is calculated from the IUI procedure date + 266 days, which is the same as adding 280 days to an estimated LMP. This calculator supports IUI date calculation.
Yes. Dr. Rukkayal Fathima is a qualified obstetrician (MS OBG, MRCOG UK) with experience managing high-risk pregnancies including those conceived through IVF, IUI, and other assisted techniques.
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Dr. Rukkayal Fathima provides personalised obstetric care from early pregnancy through delivery.
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