How to Calculate Your Due Date
Finding out your estimated due date is one of the most exciting moments of pregnancy. This calculator uses Naegele rule, the standard medical method, to estimate when your baby will arrive. You can calculate from either your last menstrual period (LMP) or your conception date.
From LMP, the calculator adds 280 days (40 weeks). From conception, it adds 266 days (38 weeks). The two-week difference accounts for the time between the start of your period and ovulation.
Due Date Calculation Methods
- Last Menstrual Period (LMP): Due Date = LMP + 280 days. This is the standard method used by most healthcare providers.
- Conception Date: Due Date = Conception + 266 days. More accurate if you know when conception occurred.
- Ultrasound Dating: An early ultrasound can measure the embryo and provide the most accurate estimate, especially if your cycles are irregular.
How to Use This Calculator
- Choose your method: Select LMP or conception date.
- Enter the date: Input the month, day, and year.
- Click Calculate: See your estimated due date, current week, trimester, and important milestones.
Pregnancy Milestones by Trimester
- First Trimester (Weeks 1-12): Heart begins beating (week 6), all major organs forming, morning sickness common.
- Second Trimester (Weeks 13-26): Baby begins moving (weeks 16-20), gender can be determined, energy often returns.
- Third Trimester (Weeks 27-40): Baby gains weight rapidly, lungs mature, preparation for delivery.
Important Prenatal Tips
- Start prenatal vitamins: Folic acid is especially important in early pregnancy.
- Schedule regular checkups: Follow your healthcare provider recommended visit schedule.
- Stay active: Moderate exercise is beneficial for most pregnancies.
- Eat a balanced diet: Focus on whole foods, lean proteins, and plenty of fruits and vegetables.
- Stay hydrated: Aim for 8-10 glasses of water daily during pregnancy.
Pregnancy Due Date Calculator FAQ
How is my due date calculated?
The most common method uses Naegele rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). If using the conception date, add 266 days (38 weeks). Only about 5% of babies are born on their exact due date.
How accurate is a due date calculator?
Due date calculators provide an estimate. Most babies are born within two weeks before or after the due date. An early ultrasound (before 12 weeks) is the most accurate method for dating a pregnancy, often more precise than LMP-based calculations.
What are the three trimesters?
The first trimester spans weeks 1-12, the second trimester weeks 13-26, and the third trimester weeks 27-40. Each trimester involves different developmental milestones for the baby and physical changes for the mother.
When should I see a doctor after finding out I am pregnant?
Schedule your first prenatal visit between weeks 6-8 of pregnancy. This visit typically includes confirming the pregnancy, estimating the due date via ultrasound, running blood tests, and discussing prenatal vitamins and care.
Can my due date change?
Yes, your due date may be adjusted after an early ultrasound measurement if it differs significantly from the LMP calculation. Due dates can also shift if your menstrual cycles are irregular or if the exact date of your last period is uncertain.