Baby Due Date Calculator
Calculate your estimated due date.
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Result
What is a Baby Due Date Calculator?
A Baby Due Date Calculator estimates when your baby will arrive based on the first day of your last menstrual period (LMP) and your average cycle length. It uses the standard Nägele’s rule to give you a 40-week estimate.
How to calculate baby due date manually (the formula)
Nägele’s rule: EDD = LMP + 280 days + (cycle length − 28).
Take the first day of your LMP, add 280 days (40 weeks), then add or subtract the difference between your cycle length and 28 days. For a 28-day cycle, simply add 280 days.
Example calculation
LMP = 1 June 2025, cycle = 30 days. EDD = 1 June + 280 + (30 − 28) = 1 June + 282 days = 10 March 2026.
Common mistakes
- Using the due date from a previous pregnancy — Every pregnancy is different. Always calculate based on the current pregnancy’s LMP.
- Not accounting for irregular bleeding — Spotting or breakthrough bleeding can be mistaken for a period. If you are unsure, an ultrasound is more reliable than LMP.
- Forgetting that the due date is an estimate — Only 1 in 20 babies is born on their due date. Use the date as a planning guide, not a deadline.
Frequently asked questions
What is a baby due date?
A baby due date is the estimated date of delivery, calculated 40 weeks (280 days) from the first day of your last menstrual period. It is a guideline, not a prediction.
How is the due date calculated?
The standard method is Nägele’s rule: LMP + 280 days. The calculator adjusts for your cycle length if it differs from 28 days.
How accurate is a due date?
Only about 5% of babies are born on their exact due date. Full-term is 37 to 42 weeks. The due date is a midpoint estimate, not a fixed appointment.
What if I don’t know my LMP?
If you don’t know your LMP, an early ultrasound (before 12 weeks) can estimate gestational age by measuring the baby’s crown-rump length.
Can I have a due date range instead of a single day?
Yes. Your estimated window is typically 37–42 weeks from LMP. The calculator gives a single midpoint, but the actual delivery can happen anytime in that window.
How does cycle length affect the due date?
A longer cycle shifts ovulation and conception later, so the due date is later. A shorter cycle shifts it earlier. Each day of cycle difference changes the due date by one day.