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How to Calculate Your Due Date
Our calculator supports two methods:
Method 1: Last Menstrual Period (LMP) — Most Common
Enter the first day of your last period and your average cycle length. This is the standard method used by healthcare providers worldwide.
The formula (Naegele’s rule):
Due Date = LMP + 280 days (40 weeks)
For cycle lengths other than 28 days, we adjust the ovulation estimate accordingly.
Method 2: Conception Date
If you know when you conceived (via IVF, ovulation tracking, or a known date), enter it directly. We add 266 days (38 weeks from conception) to calculate the due date.
How Pregnancy Weeks Are Counted
Pregnancy is measured in weeks from your last menstrual period — not from conception. This means:
- At conception, you’re considered “2 weeks pregnant” (based on a 28-day cycle)
- A full-term pregnancy is 40 weeks from LMP (38 weeks from conception)
The Three Trimesters
| Trimester | Weeks | Key Developments |
|---|---|---|
| First | 1–12 | Organ formation; most sensitive to teratogens; highest miscarriage risk |
| Second | 13–26 | Rapid growth; baby starts moving; anatomy scan |
| Third | 27–40 | Lung maturation; baby gains weight; prepares for birth |
Important Pregnancy Milestones
| Week | Milestone |
|---|---|
| 6 | Heartbeat detectable by ultrasound |
| 10 | NIPT genetic screening available |
| 12 | End of first trimester; risk of miscarriage drops significantly |
| 18–20 | Anatomy scan ultrasound |
| 20 | Halfway point; baby can hear sounds |
| 24 | Viability milestone — baby has a chance of survival outside the womb with intensive care |
| 28 | Third trimester begins; glucose tolerance test |
| 36 | Weekly prenatal appointments begin |
| 37 | Full-term pregnancy |
| 40 | Estimated due date |
How Accurate Is the Due Date?
Only 5% of babies are born on their exact due date. The “due date” is really a due range:
- 37–42 weeks is considered normal
- 70% of babies are born within 10 days of the estimated date
- 90% are born within 2 weeks
Your due date may be adjusted after your dating ultrasound (usually at 10–13 weeks), which is considered more accurate than LMP for irregular cycles.
How Does My Due Date Compare to Others?
December and September are the most common birth months in the Northern Hemisphere. If you’re due in those months, expect birthing centres to be busy!
What to Do After Calculating Your Due Date
- Schedule your first prenatal appointment — ideally between 8–10 weeks
- Start prenatal vitamins if you haven’t already — folic acid is critical in the first 12 weeks
- Notify your employer and check maternity/paternity leave policies
- Research your birth options — hospital, birth centre, or home birth
- Create a birth plan — understand your preferences and discuss with your provider
Disclaimer
This calculator provides an estimated due date based on general formulas. Individual pregnancies vary. Always consult your midwife or obstetrician for medical advice and your officially confirmed due date.
Calculate My Baby's Due DateRelated Tools:
- Period Calculator — track your menstrual cycle
- Age Calculator — calculate exact age in weeks, months, and days
- Date Duration Calculator — count days between any two dates