Due Date Calculator
Estimate your pregnancy due date from your last menstrual period or conception date.
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Due Date Calculator
Use the formula and worked example below to calculate manually.
Overview
The due date calculator estimates your pregnancy due date (Estimated Due Date / EDD) using Naegele's Rule — by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP).
How to use this calculator
- Enter the first day of your last menstrual period (LMP).
- Alternatively, enter the conception date if known.
- The calculator shows the estimated due date, current week of pregnancy, and the trimester you're in.
Understanding the inputs & results
LMP (Last Menstrual Period)
The first day of your last period before conception. Used as the standard starting point for calculating gestational age.
EDD (Estimated Due Date)
The expected date of delivery, typically 280 days (40 weeks) from LMP.
Gestational age
Age of the pregnancy measured from the first day of the LMP, in weeks and days.
Trimester
Pregnancy is divided into three trimesters: 1st (0–13 wks), 2nd (14–27 wks), 3rd (28–40 wks).
The formula
Naegele's Rule
EDD = LMP + 280 days (or LMP + 9 months + 7 days)
Add 280 days to the first day of the last menstrual period. Equivalently, add 9 months and 7 days to the LMP. Only about 5% of babies are born exactly on the EDD.
Worked example
LMP: 1 January 2025.
- EDD = 1 Jan + 280 days = 8 October 2025.
- Or: 1 Jan + 9 months + 7 days = 8 October 2025.
✓ Estimated Due Date: 8 October 2025.
Frequently asked questions
This calculator is for informational purposes only and is not a substitute for professional prenatal care. Consult your OB-GYN or midwife for medical advice and accurate dating by ultrasound.