Due Date
Due Date — runs in your browser. Inputs are not stored.
Due date (Naegele)
Enter values, then press Calculate.
Naegele’s rule (LMP + 1 year − 3 months + 7 days ≈ 280 days). For reference only; not a medical diagnosis.
How to use
- Enter the first day of the last menstrual period (LMP).
- Press Calculate to see the due date and the rule (LMP + 280 days).
- Naegele’s rule is LMP + 1 year − 3 months + 7 days, essentially a 280-day assumption.
- For week number and D-Day, use the pregnancy week calculator. This screen focuses on one date.
- Actual birth often moves around the due date. This is not a medical diagnosis—follow your obstetrician.
Key concepts
The due date calculator is for estimated delivery date using Naegele’s rule. It adds 280 days to the first day of the last period. It assumes a 28-day cycle, so longer or shorter cycles can be off. Use the pregnancy week tool for week display. Ultrasound EDC can differ.
Twins, irregular ovulation, and IVF should follow the hospital. This is not a medical diagnosis. Only the date is added locally. If the cycle is not 28 days or an ultrasound EDC exists, the hospital date is the one to use. Actual delivery often differs. For gestational weeks, use the pregnancy week calculator.
Example
LMP 2026-01-01 gives due date 2026-10-08 (January 1 + 280 days). LMP 2026-06-15 is around 2027-03-22. Leap years and month-end dates roll over via the browser Date. A few days’ difference from the hospital due date is common. LMP 2025-12-01 → 2026-09-07. LMP 2026-03-10 → 2026-12-15. Month-end rollover follows calendar rules.
Notes
This result is not medical diagnosis or treatment advice. Discuss health, pregnancy, and nutrition with a clinician. The due date is for reference and may differ from the actual birth date.
Related: Pregnancy week calculator · Calorie calculator (BMR·TDEE) · Water intake calculator
Frequently asked questions
Why is the due date 280 days?
It is a common pregnancy-length assumption, in the same spirit as Naegele’s rule. 280 days is a traditional assumption.
Does the due date calculator also show pregnancy weeks?
Use the pregnancy week calculator for weeks. This tool only shows the due date. Week and D-Day tables are not on this screen.
Is the due-date calculation sent to a server?
No. Addition runs only in the browser. LMP is not transmitted.
How accurate is the due date calculator?
It is for reference and can differ from actual birth. Follow the hospital. ±2 weeks around the due date is common—do not treat this date as a confirmed delivery day.
Is this tool a medical diagnosis?
No. It is not medical advice.
My cycle is 35 days. How should I set the due date?
This screen is fixed at 280 days. Ask obstetrics for cycle adjustment. Cycle-length correction is not included.
Last reviewed: 2026-09-04