Free Online Calculators
Due date by Naegele's rule, pregnancy week & trimester
Wondering when your little one will arrive? Our free due date calculator gives you an estimated delivery date in seconds. Simply enter the first day of your last menstrual period (LMP) and get your due date calculated using Naegele's rule – the same method used by most healthcare providers worldwide.
The most widely used method for estimating a due date is Naegele's rule, developed by German obstetrician Franz Karl Naegele in the 19th century. It works by taking the first day of your last menstrual period, adding one year, subtracting three months, and adding seven days. This gives you an estimated due date based on a standard 28-day cycle and a 40-week pregnancy.
In simple terms:
Keep in mind that only about 5% of babies are born exactly on their due date. Most babies arrive within two weeks before or after the estimated date, so think of it as a target window rather than a guaranteed calendar appointment.
Once you know your due date, you can track exactly how far along you are in your pregnancy. Our calculator shows your current pregnancy week, the number of days remaining, and which trimester you're in right now.
The first trimester covers the first three months of pregnancy. This is a critical period of development when your baby's major organs, nervous system, and facial features begin to form. Many people experience morning sickness, fatigue, and breast tenderness during this time.
Often called the "honeymoon phase" of pregnancy, the second trimester typically brings relief from early symptoms. Your bump becomes visible, and around week 18–22 you may feel your baby move for the first time – a moment known as quickening. This is also when many parents find out the baby's sex during an anatomy scan.
The final stretch! During the third trimester, your baby gains most of their birth weight and moves into position for delivery. You may feel Braxton Hicks contractions, increased back pain, and more frequent trips to the bathroom. At week 37, your pregnancy is considered full term.
If you're unsure of your LMP, don't worry – you still have options. An ultrasound scan performed during the first trimester is actually the most accurate way to date a pregnancy. Your healthcare provider will measure the fetus and calculate gestational age based on size. In later pregnancy, dating becomes less precise, which is why early prenatal visits are so important.
While Naegele's rule is a reliable starting point, it assumes a regular 28-day cycle with ovulation on day 14. If your cycles are longer, shorter, or irregular, your due date may need to be adjusted. That's why your doctor might revise your EDD after your first ultrasound – and that's completely normal. Trust your healthcare team to give you the most accurate date based on all available information.
Our calculator uses Naegele's rule, which is the standard clinical method for estimating due dates. It's a reliable estimate for women with regular 28-day cycles. However, due dates are always estimates – only about 5% of babies are born on their predicted date. An early ultrasound remains the gold standard for accurate pregnancy dating.
The first trimester runs from week 1 to week 12. The second trimester starts at week 13 and ends at week 26. The third trimester begins at week 27 and continues until birth, typically around week 40.
Yes, but with a slight adjustment. For IVF pregnancies, due dates are typically calculated from the egg retrieval date (add 266 days) or the embryo transfer date (add 263 days for a day-3 transfer, or 261 days for a day-5 transfer). Consult your fertility clinic for the most accurate dating.
A pregnancy is considered full term at 39–40 weeks. Babies born at 37–38 weeks are called "early term," while those born at 41 weeks are "late term" and at 42+ weeks are "post-term." Full-term babies generally have the best outcomes in terms of development and health.
Absolutely. Our due date calculator is a helpful planning tool, but it is not a substitute for professional medical advice. Schedule your first prenatal appointment as soon as possible after a positive pregnancy test. Early prenatal care is one of the most important steps you can take for a healthy pregnancy and baby.