Pregnancy Calculator
Calculate due date and pregnancy milestones from your last period
Estimated Due Date
How to Use
- Select the first day of your last menstrual period using the date picker.
- Click 'Calculate' to compute your estimated due date.
- View your current gestational age in weeks and days.
- See how many days remain until your estimated due date.
- Review the trimester timeline and key pregnancy milestones.
About Pregnancy Calculation
Naegele's Rule
Naegele's rule is the standard method for calculating an estimated due date. The formula adds 280 days (40 weeks) to the first day of the last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14. The formula was developed by Franz Karl Naegele in the early 19th century and remains in widespread clinical use.
Gestational Age
Gestational age is counted from the first day of the last menstrual period, not from conception. This means pregnancy is considered to begin 2 weeks before actual conception. A full-term pregnancy is 40 weeks (280 days) from LMP. Babies born between 37 and 42 weeks are considered full-term.
Trimesters
Pregnancy is divided into three trimesters. The first trimester (weeks 1–12) involves rapid organ development and has the highest risk of miscarriage. The second trimester (weeks 13–26) is typically the most comfortable. The third trimester (weeks 27–40) involves rapid fetal growth and preparation for birth.
Accuracy of Due Date
Only about 5% of babies are born on their exact due date. Most births occur within 2 weeks before or after the estimated date. An early ultrasound (before 14 weeks) provides the most accurate dating by measuring fetal size. Due date accuracy decreases with irregular menstrual cycles.
Key Features
- Calculates due date using Naegele's rule
- Shows current gestational age in weeks and days
- Displays trimester information and key milestones
- Counts down days remaining until due date