Pregnancy Due Date Calculator
Estimate your baby's due date, find out how many weeks pregnant you are, and see your trimester and key milestones — based on your last menstrual period or conception date.
Calculate Your Due Date
Choose a method, enter the relevant date, and get your estimated delivery date instantly.
How the Due Date Is Calculated
Your estimated due date (EDD) is the date your baby is expected to arrive — around 40 weeks after the first day of your last menstrual period. The most widely used method, known as Naegele's rule, simply adds 280 days (40 weeks) to the first day of your last period. If instead you know the date you conceived or ovulated, the due date is calculated as that date plus 266 days (38 weeks), because conception typically happens about two weeks after your period starts.
Why a Full-Term Pregnancy Is 40 Weeks
It may seem odd that pregnancy is counted as 40 weeks when conception happens about two weeks into that count. This is because doctors measure pregnancy from the first day of your last menstrual period — a date that is easy to remember — rather than from the moment of conception, which is hard to pinpoint exactly. As a result, "gestational age" is roughly two weeks more than the embryo's true age. A pregnancy is considered full term anywhere between 37 and 42 weeks.
The Three Trimesters
- First trimester (weeks 1–12): The baby's major organs and structures form. Many mothers experience morning sickness and fatigue during this period.
- Second trimester (weeks 13–26): Often the most comfortable phase. The baby grows rapidly, movement begins to be felt, and the sex may be visible on ultrasound.
- Third trimester (weeks 27–40): The baby gains weight and prepares for birth. The mother may feel increased discomfort as the due date approaches.
How Accurate Is a Due Date?
A due date is an estimate, not a deadline. Only about 4% of babies arrive on their exact predicted date, and a perfectly healthy delivery can happen any time within the 37-to-42-week full-term window. Cycle length, the precise timing of ovulation and natural variation between pregnancies all influence the actual delivery date. An early dating ultrasound — usually performed between weeks 8 and 13 — is generally the most accurate way to confirm or adjust your due date.
Adjusting for Cycle Length
The standard 280-day calculation assumes a regular 28-day menstrual cycle with ovulation on day 14. If your cycles are consistently longer or shorter, the LMP-based due date can be off by several days. This calculator lets you enter your average cycle length so the estimate can be adjusted accordingly. If your cycles are irregular, the conception-date method or an ultrasound will give a more reliable result.
What to Do After Estimating Your Due Date
- Book prenatal care early: Schedule your first appointment with an obstetrician as soon as possible.
- Plan key scans: The dating scan, anomaly scan (around week 20) and growth scans are important milestones.
- Track your weeks: Knowing your gestational age helps you follow your baby's development week by week.
- Prepare gradually: Use the months ahead to plan finances, leave, and hospital arrangements.
Important: This calculator provides a general estimate for informational purposes only and is not a substitute for professional medical advice. Always consult a qualified obstetrician or gynaecologist to confirm your due date and monitor your pregnancy.
Frequently Asked Questions — Pregnancy Due Date Calculator
The most common method (Naegele's rule) adds 280 days — exactly 40 weeks — to the first day of your last menstrual period (LMP). This assumes a regular 28-day cycle with ovulation on day 14. If you know your conception or ovulation date instead, the due date is that date plus 266 days (38 weeks). This calculator supports both methods.
A due date is an estimate, not a guarantee. Only about 4% of babies are born on their exact due date, and a full-term delivery can occur anytime between 37 and 42 weeks. Factors like cycle length, the exact date of ovulation and individual variation all play a role. Your doctor may revise the date after an early ultrasound, which is often the most accurate method.
Pregnancy is divided into three trimesters. The first trimester runs from week 1 to the end of week 12, the second from week 13 to the end of week 26, and the third from week 27 until birth (around week 40). Each trimester brings distinct developmental milestones for the baby and physical changes for the mother.
The LMP method assumes a 28-day cycle, so it may be less accurate if your cycles are irregular or significantly longer or shorter. If you know your conception or ovulation date, use that option for a better estimate. In all cases, an early dating ultrasound performed by your doctor gives the most reliable due date.
Gestational age is how far along your pregnancy is, measured in weeks and days from the first day of your last menstrual period. It is the standard way doctors track pregnancy progress. Note that gestational age is about two weeks more than the actual age of the embryo, because counting starts from the LMP rather than from conception.
No. This tool provides a general estimate for informational purposes only. It is not a substitute for professional prenatal care. Always confirm your due date and monitor your pregnancy with a qualified obstetrician or gynaecologist, who can account for your individual health and ultrasound findings.