Free Pregnancy Due Date Calculator
Estimated due date from last menstrual period (Naegele's rule).
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Result
Estimated due date
Thursday, October 8, 1970
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Short answer
Estimated due date is the first day of the last menstrual period plus 280 days (40 weeks). This assumes a 28-day cycle with ovulation on day 14.
What is the Pregnancy Due Date Calculator?
An estimated delivery date based on the last menstrual period. Modern practice confirms with an early ultrasound.
How does the Pregnancy Due Date Calculator work?
Add 280 days to the first day of the last period. Adjust up or down if the cycle length differs from 28 days.
Formula
Variables
LMPFirst day of last menstrual periodcycleTypical cycle length in days
Explanation
Naegele's rule with a cycle-length correction. Only about 4% of babies arrive on the exact EDD.
Examples
Example 1: LMP Jan 1, 28-day cycle
EDD Oct 7, conception ~Jan 15.
Applications
- Prenatal appointment scheduling
- Maternity leave planning
- Trimester tracking
Advantages
- Simple, well-established
- Cycle-length correction improves accuracy
Limitations
- Only about 4% deliver on the EDD exactly
- Ultrasound-based dating in first trimester is more accurate
Common mistakes
- Using the last day of period instead of first day
Tips
- Confirm with a first-trimester dating scan
Related concepts
The Pregnancy Due Date Calculator sits inside the Health Calculators hub, in the pregnancy & women's health cluster. Cycle, conception and gestation timelines. Understanding the terms below makes the output easier to interpret and easier to compare against neighbouring measures.
Practical use cases and industry applications
Understanding Pregnancy Due Date
An estimated delivery date based on the last menstrual period. Modern practice confirms with an early ultrasound. Within health calculators, pregnancy due date belongs to the pregnancy & women's health cluster, where it shares terminology and assumptions with closely related tools.
Learning how pregnancy due date is calculated
Naegele's rule with a cycle-length correction. Only about 4% of babies arrive on the exact EDD. Working through the variables one at a time — LMP, cycle — makes the result reproducible by hand and easier to sanity-check.
Using pregnancy due date to make a decision
Prenatal appointment scheduling Maternity leave planning Trimester tracking Because outputs depend on the assumptions you enter, run more than one scenario before committing to a figure.
How pregnancy due date compares with related measures
gestational age, luteal phase, fertile window, trimester all describe adjacent aspects of pregnancy & women's health. Comparing this calculator's output against those measures — using the related tools listed on this page — prevents a single metric from being read in isolation.
Frequently asked questions
Is my due date guaranteed?
No — it is an estimate. Full-term deliveries range 37–42 weeks. About 95% of babies arrive within two weeks of the EDD.
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