Due Date Calculator
Estimates delivery by adding 280 days to first day of LMP. Adjusts for cycle length difference from 28-day standard.
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How It Works
Estimates delivery by adding 280 days to first day of LMP. Adjusts for cycle length difference from 28-day standard.
Quick Reference
LMP Jan 1
+280 days
Due Oct 8
LMP March 15
+280 days
Due Dec 20
Normal delivery window
37-42 weeks
5-week range
Tips & Shortcuts
Early ultrasound at 8-12 weeks is most accurate.
Normal delivery: 37-42 weeks. Only 5% on exact due date.
Common Mistakes
Treating due date as guaranteed delivery date
Due date is 40-week estimate. Normal range spans 5 weeks.
Not adjusting for irregular cycle
Longer cycles push due date later.
Frequently Asked Questions
The standard method adds 280 days (40 weeks) to the first day of your last period. This is Naegele's Rule, used globally.
For day-5 embryo transfer, add 261 days. For day-3, add 263 days. For day-6, add 260 days. IVF due dates are typically more precise than LMP-based estimates.
A first-trimester ultrasound (7–13 weeks) is accurate within ±5–7 days — more reliable than LMP dating, especially for irregular periods.
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