Estimate your baby's due date with our free online Pregnancy Due Date Calculator. This comprehensive tool uses Naegele's Rule — the standard method used by obstetricians and midwives worldwide — to calculate your estimated due date (EDD) based on the first day of your last menstrual period (LMP) and your average menstrual cycle length. Naegele's Rule, developed by German obstetrician Franz Naegele in 1812, estimates the due date by adding 280 days (40 weeks) to the first day of the last menstrual period. This calculation assumes a standard 28-day menstrual cycle with ovulation occurring on day 14. Since not everyone has a 28-day cycle, our calculator allows you to input your actual cycle length and adjusts the due date accordingly — for every day your cycle is longer or shorter than 28 days, the due date shifts by one day. Our calculator provides much more than just the due date. It also displays your current gestational age in weeks and days, which trimester you are in, the number of days remaining until your due date, and a visual progress bar showing how far along you are in your pregnancy journey. Pregnancy is divided into three trimesters, each with distinct developmental milestones: • First Trimester (Weeks 1–12): During this critical period, the embryo develops all major organ systems. By week 6, the heart begins beating. By week 12, the fetus is about 6 cm long and has developed fingers, toes, and facial features. This trimester is when morning sickness and fatigue are most common. • Second Trimester (Weeks 13–26): Often called the 'golden period' of pregnancy, many women experience relief from early symptoms. The fetus grows rapidly, begins making purposeful movements (quickening), and develops hearing capability. An anatomy ultrasound is typically performed around week 20. • Third Trimester (Weeks 27–40): The fetus gains significant weight, develops mature lungs, and prepares for birth. The mother may experience Braxton Hicks contractions, increased fatigue, and sleep difficulties. Babies born after 37 weeks are considered full-term. It is important to understand that the 'due date' is an estimate, not a guarantee. Only about 4% of babies are born exactly on their due date. Most births occur within a two-week window around the EDD — anywhere from 38 to 42 weeks is considered normal. First-time mothers are statistically more likely to deliver past their due date, while subsequent pregnancies may arrive earlier. Several factors can affect the accuracy of due date calculations based on LMP. If you have irregular menstrual cycles, do not remember the exact date of your last period, recently stopped hormonal contraception, or have cycles significantly longer or shorter than 28 days, an early ultrasound (typically performed between 8–12 weeks) provides the most accurate dating. Ultrasound dating measures the crown-rump length (CRL) of the embryo and is accurate to within ±5 days in the first trimester. Our calculator is intended as an informational tool only and should not replace professional medical advice. Every pregnancy is unique, and your healthcare provider will consider multiple factors — including ultrasound measurements, medical history, and physical examination — to determine the most accurate due date for your situation. The tool includes a medical disclaimer and processes all data entirely in your browser. No pregnancy-related information is stored, transmitted, or shared with any third party. It is completely free to use, works on all devices, and requires no account creation. Use it to get a quick estimate and track your pregnancy week by week.
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