Pregnancy Due Date Calculator 2025
Calculate your estimated due date using your last menstrual period (LMP) or conception date. Get detailed pregnancy information including weeks pregnant, trimester, and delivery timeline.
How to Calculate Your Pregnancy Due Date
The pregnancy due date is an estimate of when your baby will be born. Most pregnancies last about 280 days (40 weeks) from the first day of your last menstrual period (LMP). However, only about 5% of babies are born exactly on their due date!
Naegele's Rule: The Standard Method
The most common method for calculating due date is Naegele's Rule. Simply add 280 days (40 weeks) to the first day of your last menstrual period. For example, if your LMP was January 1, your due date would be approximately October 10 of that year.
LMP vs. Conception Date
Most healthcare providers use your LMP (Last Menstrual Period) to calculate your due date because it's usually easier to remember than the actual date of conception. Conception typically occurs about 14 days after the start of your last period. If you know your conception date, subtract 14 days to estimate your LMP.
The Three Trimesters
Pregnancy is divided into three trimesters, each approximately 13 weeks long:
First Trimester (Weeks 1-13): Organ formation, morning sickness, fatigue
Second Trimester (Weeks 14-27): Baby becomes more active, you may start showing
Third Trimester (Weeks 28-40): Rapid growth, baby positions for delivery
Full-Term vs. Preterm Delivery
Full-term pregnancy: 37 weeks or more (weeks 37-42 are considered full-term)
Preterm delivery: Before 37 weeks (may require NICU care)
Post-term pregnancy: Beyond 42 weeks (doctors may induce labor)
The earliest safe delivery is around 24 weeks (viability), and the latest is 42 weeks.
Frequently Asked Questions
Pregnancy due date is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). This method is called Naegele's Rule. If you know your conception date, you can add 266 days (38 weeks) instead. Due dates are estimates—only about 5% of babies arrive exactly on their due date.
LMP (Last Menstrual Period) is the first day of your last period before pregnancy. Conception typically occurs about 14 days after LMP. Medical professionals use LMP for due date calculation because it's usually easier to remember. If you know your LMP, conception was approximately 14 days later.
First Trimester (Weeks 1-13): Organ formation, morning sickness, and fatigue.
Second Trimester (Weeks 14-27): Continued development, "quickening" (feeling baby move), and increased energy.
Third Trimester (Weeks 28-40): Rapid growth, preparation for birth, and increased discomfort.
Yes. Delivery between weeks 37-42 is considered full-term and safe. About 8-10% of pregnancies deliver before 37 weeks (preterm). Babies born at 24+ weeks have a chance of survival with medical support. Delivery 1-2 weeks after your due date is also normal, but doctors typically induce labor if you go past 42 weeks.
If you don't know your exact LMP, talk to your healthcare provider. They can estimate your due date using an ultrasound, which is most accurate in the first trimester (within 3-5 days). As pregnancy progresses, ultrasound estimates become less precise, so first-trimester dating is preferred.
Fetal viability typically occurs around 20-24 weeks of pregnancy. This is the point where a baby could potentially survive outside the womb with intensive medical care. However, babies born after 36-37 weeks have much higher survival rates and better health outcomes. This calculator marks week 20 as the viability milestone.