Pregnancy Due Date Calculator

Estimate your baby's due date instantly. Enter your last period or conception date and get your estimated due date and current week.

About this tool

Estimating a pregnancy due date is one of the first things many expectant parents want to do after a positive pregnancy test. The most widely used method is based on **Naegele's Rule**, which adds approximately 280 days (40 weeks) to the first day of the last menstrual period (LMP). This approach assumes a standard 28-day menstrual cycle, which is why our calculator also takes your average cycle length into account — adding or subtracting days proportionally when your cycle is longer or shorter than 28 days. It is important to understand that this calculated date is an **estimate**, often called an Estimated Due Date (EDD) or Expected Date of Delivery (EDD). In practice, only a small percentage of babies are born exactly on their due date. Most full-term pregnancies result in birth within a window of a few weeks on either side of the EDD. Healthcare providers typically consider a pregnancy "full term" somewhere between 39 and 40 weeks, though the specific definitions can vary by provider and medical guidelines. The 40-week timeline is conventionally divided into three trimesters. The first trimester covers roughly the first 13 weeks and is when foundational organ development occurs. The second trimester, from about week 14 to week 26, is when many people begin to feel fetal movement. The third trimester runs from around week 27 until birth, a period focused on growth and preparation for delivery. For the most accurate dating of a pregnancy, healthcare professionals often rely on an **ultrasound scan**, particularly one performed in the first trimester. Ultrasound can measure the size of the embryo or fetus and provide a more precise gestational age estimate, especially when the date of the last menstrual period is uncertain or when cycles are irregular. This calculator is provided as a general informational tool and is **not a substitute for professional medical advice**. Always consult a qualified healthcare provider to confirm your due date, monitor your pregnancy, and address any health concerns. Individual pregnancies vary, and your provider will use a combination of your medical history, physical exams, and imaging to guide your care throughout the pregnancy journey.

FAQ

Q. How is the estimated due date calculated?
A. The most common method is Naegele's Rule, which adds 280 days (40 weeks) to the first day of your last menstrual period. Our calculator also adjusts this figure based on your average cycle length, since longer or shorter cycles can shift the estimated ovulation date and therefore the due date.
Q. How accurate is an estimated due date?
A. A calculated due date based on LMP is an estimate. Only a small proportion of babies arrive on the exact predicted date. Most are born within a window of several weeks around the EDD. A first-trimester ultrasound is generally considered a more precise method for confirming gestational age.
Q. What if I don't know the exact date of my last period?
A. If you are unsure of your LMP, try to recall approximately when it started and use that as a rough estimate. Your healthcare provider can use an early ultrasound to better determine how far along you are and refine your estimated due date accordingly.
Q. Does a longer or shorter cycle affect my due date?
A. Yes. The standard 280-day calculation assumes a 28-day cycle. If your cycle is regularly longer, ovulation tends to occur later, which can push the due date further out. If your cycle is shorter, the estimated due date may be earlier. Our calculator accounts for this by adjusting the LMP start point based on the difference between your cycle length and 28 days.
Q. Should I rely on this calculator instead of seeing a doctor?
A. No. This tool is intended for general informational purposes only and is not a replacement for professional prenatal care. A qualified healthcare provider will confirm your due date, monitor the health of both you and your baby, and guide you through your pregnancy with personalized medical advice.

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