Pregnancy Calculator
Calculate your due date and track your pregnancy progress
How Is a Due Date Calculated?
This calculator uses Naegele's Rule, the standard obstetric method for estimating due dates. The rule is simple: add 280 days (40 weeks) to the first day of your Last Menstrual Period (LMP). This formula was developed by German obstetrician Franz Karl Naegele in the early 19th century and remains the basis for due date estimation in modern obstetrics worldwide.
The 280-day figure assumes a regular 28-day menstrual cycle with ovulation occurring on day 14. If your cycle is shorter or longer, your actual conception date — and therefore your due date — may differ by several days. Ultrasound dating, particularly during the first trimester, is the most accurate method and may adjust the estimate provided here.
About 80% of babies are born within 2 weeks before or after their estimated due date. Only about 5% of babies are born exactly on their due date. Early (before 37 weeks) and late (after 42 weeks) deliveries require medical management.
The Three Trimesters of Pregnancy
Pregnancy is divided into three 13-week periods called trimesters. Each has distinct developmental milestones and maternal experiences:
First Trimester (Weeks 1–13)
This is the most critical period for fetal development. By the end of the first trimester, all major organs have begun forming — heart, brain, spinal cord, and limbs. This is also when the risk of miscarriage is highest (about 80% of miscarriages occur in the first trimester). Common symptoms include morning sickness, fatigue, breast tenderness, and frequent urination. Prenatal vitamins with folic acid (400–800 mcg/day) are especially important during this period.
Second Trimester (Weeks 14–27)
Often called the "honeymoon trimester," many women experience relief from morning sickness and increased energy levels. The baby becomes recognizable on ultrasound, and fetal movement (quickening) is typically felt between weeks 18 and 25. This trimester includes the anatomy scan (typically at 18–20 weeks) to check fetal development.
Third Trimester (Weeks 28–40)
The baby undergoes rapid growth in weight and size — going from about 2.2 lbs at 28 weeks to a full-term weight of 6–8 lbs. The lungs mature, and the baby repositions head-down in preparation for birth. Symptoms include back pain, shortness of breath, swollen ankles, and Braxton Hicks contractions. Babies born after 37 weeks are considered full-term.
Frequently Asked Questions
Can I use this if I used IVF or fertility treatments? IVF pregnancies are dated from the egg retrieval date (add 266 days) rather than the LMP. Speak with your fertility specialist who will provide a precise due date.
What is a gestational age vs fetal age? Gestational age counts from your LMP (so you are technically already "2 weeks pregnant" at the time of conception). Fetal age counts from actual conception and is 2 weeks less than gestational age.
⚠️ Medical Disclaimer: This calculator provides an estimated due date for informational purposes only. Due dates can change based on ultrasound measurements and other clinical factors. Always confirm your due date and track your pregnancy progress with a qualified obstetrician, midwife, or healthcare provider.