The moment a pregnancy test shows positive, every parent-to-be asks the same question: “Baby kab aayega?” Your due date — also called the Estimated Date of Delivery (EDD) — anchors your whole pregnancy journey: scans, check-ups, and leave plans are all scheduled around it. Our free due date calculator uses Naegele’s rule, the standard obstetric method since the 1800s, to estimate your delivery date from the first day of your last menstrual period (LMP) — and tells you how far along you are today.
Pregnancy Due Date Calculator
Estimate your due date from the first day of your last menstrual period.
Naegele’s Rule — How the Date Is Worked Out
Due date = LMP + 280 days (equivalently: LMP + 1 year − 3 months + 7 days).
The 280 days represent the average human gestation (40 weeks) counted from the last period — conception usually happens about 14 days after LMP, so the baby itself grows for roughly 266 days.
Why obstetricians use LMP: most women remember their last period’s first day, while the exact conception date is rarely known. Ultrasound scans in the first trimester can refine (and if needed, adjust) the date — a dating scan at 8–13 weeks is the most accurate way to confirm it.
How to Use the Pregnancy Due Date Calculator
- Pick the first day of your last menstrual period (LMP) using the date picker.
- Click Calculate — your due date appears, plus your current week and day of pregnancy if LMP is in the past.
- Plan your key appointments (first scan, anomaly scan at ~20 weeks, glucose test at 24–28 weeks) around it — and confirm the date with your gynaecologist.
Worked Example
Last period started 1 January 2026. Due date = 1 Jan 2026 + 280 days = 8 October 2026. If today is mid-July 2026, she’s around 28 weeks — in the third trimester.
Notes Worth Knowing
- Only about 4–5% of babies arrive on the exact due date — it’s an “estimated window,” not an appointment. Most deliver within 37–42 weeks.
- Irregular cycles or forgetting your LMP? An early ultrasound dating scan beats the rule.
- Second pregnancies don’t change the formula — each pregnancy gets its own date.
- Your doctor may move the EDD if a first-trimester scan disagrees by more than a week — scans that early are precise because all babies grow at nearly the same rate then.
Frequently Asked Questions
How accurate is a due date calculator?
It’s as accurate as your LMP memory and cycle regularity allow. For regular 28-day cycles, it’s a solid estimate; first-trimester ultrasound is the gold standard for confirmation.
What if I don’t remember my last period date?
Tell your doctor honestly — they’ll rely on an early dating ultrasound instead. Never guess a date and plan around it for months.
Can I calculate the due date from the conception date?
Yes: conception date + 266 days. The LMP method (+280) is standard because LMP is more commonly known.
Is 40 weeks exact for every pregnancy?
No — full term is a range (37–42 weeks). Twins and certain conditions usually deliver earlier; your obstetrician will guide individual planning.
What week am I in right now?
The calculator shows your current week + day from LMP. Our gestational age calculator gives the same with your trimester and progress bar.
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