Pregnancy Calculator
Due Date, Gestational Age & Milestones
Enter the first day of your last menstrual period (LMP) to see your estimated due date, current week of pregnancy, and trimester timeline.
Parameters
Estimated Due Date
Understanding Your Pregnancy Timeline
This calculator uses Naegele's Rule — the standard obstetric method of adding 280 days (40 weeks) to the first day of your last menstrual period — adjusted for your typical cycle length, to estimate your due date and track your progress through each trimester.
First Trimester (Weeks 1-13)
Major organ development occurs during this period — it's also when early pregnancy symptoms and morning sickness are most common.
Second Trimester (Weeks 14-27)
Often called the most comfortable trimester — energy typically returns and the anatomy scan usually happens around week 20.
Third Trimester (Weeks 28-40)
Rapid weight gain and preparation for birth — most providers schedule more frequent check-ins during this stage.
Cycle-Length Adjustment
Naegele's Rule assumes a 28-day cycle. This tool adjusts the estimate if your average cycle is longer or shorter.
Important Limitations
- An estimate, not a guarantee: Only about 5% of babies are born exactly on their estimated due date.
- Assumes regular cycles: Irregular cycles or uncertain LMP dates make this estimate less reliable — an early ultrasound provides more accurate dating.
- Not a substitute for prenatal care: Your OB-GYN or midwife will confirm and refine your due date through exams and ultrasound.
Key Takeaways
- Based on Naegele's Rule. The standard obstetric method of LMP + 280 days, adjusted for cycle length.
- Gestational age counts from LMP, not conception. This is why "week 4" of pregnancy is typically only about 2 weeks after conception.
- Trimesters are approximate boundaries. Different sources define the exact week cutoffs slightly differently.
- Consult your provider. This timeline is a general estimate — always confirm your due date and gestational age with your OB-GYN or midwife via ultrasound.