Pregnancy Due Date Calculator
Calculate estimated due date from last period. See trimester and days remaining.
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📘 What is the Pregnancy Due Date Calculator?
This calculator estimates your due date using the standard obstetric method based on your last menstrual period (LMP), the same approach used by most doctors and midwives at an initial visit before an ultrasound provides a more precise estimate. It also shows your current week, trimester, and days remaining.
⚙️ How Due Date is calculated
Naegele's Rule — the 280-day standard
The standard estimate adds 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation around day 14, which is why it is an estimate rather than a guaranteed date — actual cycle length varies between individuals.
Why pregnancy is measured in weeks from LMP, not conception
Medically, pregnancy is dated from the first day of the last period, not the (harder to know precisely) date of conception, which typically occurs about two weeks later. This is why a pregnancy described as "6 weeks" usually means roughly 4 weeks since actual conception.
Trimester boundaries
The first trimester runs through week 13, the second trimester through week 27, and the third trimester from week 28 until birth — this calculator automatically flags which trimester you are currently in based on the date entered.
Naegele's Rule
Due date = LMP date + 280 days
🧮 Worked examples
Example — early pregnancy
Last menstrual period began exactly 6 weeks (42 days) ago.
→ Currently in week 6, first trimester, with approximately 238 days (34 weeks) remaining until the estimated due date
Example — entering third trimester
Last menstrual period began 28 weeks (196 days) ago.
→ Currently in week 28, the start of the third trimester, with approximately 84 days (12 weeks) remaining
💡 Original insights & how to use this calculator
Why your due date may shift after an ultrasound
An early ultrasound measuring fetal size often provides a more accurate estimate than LMP-based dating alone, particularly for people with irregular cycles. It is normal and expected for a doctor to adjust the due date by several days after this scan.
Planning around the estimated date
Only about 5% of babies are born on their exact estimated due date — treat this as the centre of a normal range (roughly 1–2 weeks before to 1–2 weeks after) rather than a precise prediction.
Using trimester information for milestone planning
Knowing your exact current week and trimester helps with timing common prenatal milestones — many anatomy scans, glucose screenings, and other check-ups are scheduled relative to specific weeks of pregnancy.
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💡 Expert tips
Only 5% of babies arrive exactly on the due date.
📖 Learn more on WellFiLab
Visit ↗❓ Common questions
How is EDD calculated?
Add 280 days to the first day of your last period (Naegele's Rule).
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