Pregnancy Due Date Calculator
Calculate your pregnancy due date from last menstrual period
How to Use
- Enter the first day of your last menstrual period (LMP)
- Enter your average menstrual cycle length in days (default is 28)
- Click calculate to see your estimated due date
- View your conception date, current week, and trimester
What is a Due Date?
A pregnancy due date is an estimate of when your baby will be born. It's calculated as 40 weeks (280 days) from the first day of your last menstrual period (LMP). This calculation assumes a regular 28-day menstrual cycle with ovulation occurring on day 14.
Healthcare providers use Naegele's rule to calculate the due date: add 7 days to the first day of your LMP, subtract 3 months, and add 1 year. Modern calculators adjust this formula based on your actual cycle length for more accuracy.
Pregnancy Trimesters
Pregnancy is divided into three trimesters, each lasting approximately 13 weeks:
- First Trimester (Weeks 1-13): Major organs and systems develop. Common symptoms include morning sickness and fatigue.
- Second Trimester (Weeks 14-27): You'll feel your baby move. Energy levels often improve during this period.
- Third Trimester (Weeks 28-40): Your baby gains weight rapidly. You may experience more discomfort as delivery approaches.
Understanding Conception Date
The conception date is estimated as approximately 14 days after the first day of your last menstrual period, assuming ovulation occurred mid-cycle. This is when the egg was fertilized by sperm. However, sperm can survive in the female reproductive tract for up to 5 days, so the actual conception date could vary slightly.
Ultrasound dating in early pregnancy (before 13 weeks) is the most accurate way to determine gestational age and refine your due date estimate.
Factors Affecting Due Date Accuracy
- Only about 5% of babies arrive exactly on their due date
- Most babies are born between 37 and 42 weeks of pregnancy
- Irregular menstrual cycles can affect calculation accuracy
- First-time mothers often deliver slightly later than the due date
- Multiples (twins, triplets) typically arrive earlier than singletons
- Early ultrasound (before 13 weeks) provides the most accurate dating
Frequently Asked Questions
- How accurate is the pregnancy due date calculator?
- The calculator provides a good estimate, but only about 5% of babies arrive on their exact due date. Most babies are born within 2 weeks before or after the estimated due date. Early pregnancy ultrasound (before 13 weeks) provides the most accurate dating.
- What if my menstrual cycle is irregular?
- If you have irregular cycles, the calculator may be less accurate. Your healthcare provider will likely use early ultrasound measurements to determine a more precise due date. Enter your best estimate of average cycle length, or use 28 days as a starting point.
- Can I calculate my due date if I had IVF or fertility treatments?
- This calculator is designed for natural conception. If you conceived through IVF or other fertility treatments, your doctor will calculate your due date based on the embryo transfer date or egg retrieval date, which is more accurate.
- What is the difference between conception date and LMP?
- LMP (Last Menstrual Period) is the first day of your last period before getting pregnant. Conception typically occurs about 14 days after LMP (during ovulation). Pregnancy is dated from LMP, not conception, so you're considered 2 weeks pregnant at conception.