Due Date Calculator
Your Pregnancy Timeline
Estimated Due Date
About Your Due Date
This estimated due date (EDD) is based on a 40-week pregnancy. Remember that only about 4% of babies are born on their exact due date.
What is a Due Date Calculator?
A Pregnancy Due Date Calculator is a tool used to estimate your Estimated Due Date (EDD), which is the day your baby is expected to be born. This calculation is a fundamental part of prenatal care, as it helps healthcare providers track your baby's growth and manage your pregnancy timeline.
A full-term pregnancy typically lasts around 40 weeks (280 days) from the first day of your last menstrual period (LMP) or 38 weeks (266 days) from the date of conception. Our calculator provides an accurate estimate based on these two standard methods, giving you a clear timeline for your pregnancy journey.
How the Due Date Calculator Works
This calculator provides two different methods for estimating your due date. The most common method, and the one most doctors use initially, is based on your last menstrual period.
Method 1: Last Menstrual Period (LMP) - Default
This is the standard method for calculating a due date. It assumes a 28-day menstrual cycle and that ovulation occurs on day 14. The calculation is based on Naegele's Rule.
Naegele's Rule Formula:
Due Date = (First Day of LMP) + 280 Days (40 Weeks)
Calculation with Cycle Length Adjustment:
If your cycle is longer or shorter than 28 days, the calculator adjusts the 280-day rule.
Adjusted Days = 280 + (Average Cycle Length - 28)
Due Date = (First Day of LMP) + Adjusted Days
- First Day of Last Period: October 1, 2025
- Average Cycle Length: 28 days
Calculation:
Due Date = October 1, 2025 + 280 days = July 8, 2026
Method 2: Date of Conception
If you know the exact date you conceived (for example, through ovulation tracking or fertility treatments), this method can be more accurate. A pregnancy lasts an average of 38 weeks (266 days) from the date of conception.
Conception Date Formula:
Due Date = (Date of Conception) + 266 Days (38 Weeks)
Understanding Your Pregnancy Timeline
Your pregnancy is divided into three "trimesters," each marking distinct phases of development. Our calculator also estimates your current gestational age (how many weeks pregnant you are) and which trimester you are in.
First Trimester (Week 1-13)
This is a time of rapid development. The fertilized egg implants in the uterus, and major organs and body systems begin to form. By the end of this trimester, the fetus has a heartbeat and is fully formed, though tiny.
Second Trimester (Week 14-27)
Often called the "honeymoon phase" as early pregnancy symptoms may ease. The baby grows rapidly, and you will likely begin to feel movement. Ultrasounds during this time can often reveal the baby's sex.
Third Trimester (Week 28-40+)
This is the final stretch. The baby gains weight quickly, and the brain and lungs continue to mature. The baby will "drop" into the pelvis in preparation for delivery. A pregnancy is considered full-term at 39 weeks.
Due Date Calculator FAQs
This calculator provides a high-quality estimate based on standardized formulas. However, it's important to remember that only about 4-5% of babies are born on their exact due date. The most accurate way to determine your due date is with an early first-trimester ultrasound, which your doctor will use to confirm or adjust your LMP-based date.
If your periods are irregular, the "Last Menstrual Period (LMP)" method will be less accurate because it assumes a predictable ovulation day. In this case, using the "Conception Date" method (if you know it) is a better option. If you don't know your conception date, your doctor will rely on an ultrasound to establish your official due date.
Yes. It is common for a doctor to adjust your due date after your first ultrasound, typically between 8 and 13 weeks. This ultrasound measures the baby's "crown-rump length" (CRL) and is considered the gold standard for dating a pregnancy. Your doctor will set your official due date based on this measurement, especially if it differs from your LMP-calculated date by more than 5-7 days.
This is a common point of confusion.
• Gestational Age (40 weeks) is calculated from the first day of your last menstrual period (LMP). This is the standard measurement doctors use.
• Fetal Age (38 weeks) is the actual age of the baby, calculated from the date of conception.
Gestational age is always about two weeks *ahead* of fetal age because your LMP starts about two weeks before you typically ovulate and conceive.