Due Date Calculator
Calculate your estimated due date and pregnancy milestones
How to Use This Due Date Calculator
- Select your calculation method: Last Menstrual Period or Conception Date
- Enter the appropriate date based on your selection
- Click 'Calculate Due Date' to see your estimated due date
- View your current pregnancy week and days remaining
- See trimester milestones for your pregnancy timeline
Example: If your last menstrual period began on May 1st, 2026, your estimated due date is February 5th, 2027 (280 days later). As of August 1st, you would be in week 13 of pregnancy with approximately 188 days remaining.
Tip: Only about 5% of babies arrive on their exact due date. Most are born within 2 weeks before or after. The due date is a midpoint of a normal delivery window, not a deadline.
Why Use a Due Date Calculator?
Knowing your estimated due date helps you prepare for baby's arrival, track pregnancy milestones, and ensure proper prenatal care timing throughout pregnancy.
- Planning maternity leave and work transitions
- Scheduling prenatal appointments and tests at appropriate gestational ages
- Preparing the nursery and purchasing baby supplies
- Notifying family and making travel arrangements
- Understanding which trimester you're in and what to expect
- Tracking baby's development milestones week by week
Understanding Your Results
Pregnancy lasts approximately 280 days (40 weeks) from the last menstrual period, or 266 days (38 weeks) from conception.
| Result | Meaning | Action |
|---|---|---|
| First Trimester (Weeks 1-12) | Foundation Period | Major organ development. Highest risk of miscarriage. Time for early prenatal care and genetic screening options. |
| Second Trimester (Weeks 13-26) | Growth Period | Anatomy scan around week 20. Baby begins moving noticeably. Often called the 'golden trimester' with fewer symptoms. |
| Third Trimester (Weeks 27-40) | Final Preparation | Rapid brain development. More frequent prenatal visits. Preparation for delivery. |
| Full Term (Weeks 39-40) | Ready for Birth | Baby is fully developed. Labor can safely begin anytime. Watch for signs of labor. |
Meaning: Foundation Period
Action: Major organ development. Highest risk of miscarriage. Time for early prenatal care and genetic screening options.
Meaning: Growth Period
Action: Anatomy scan around week 20. Baby begins moving noticeably. Often called the 'golden trimester' with fewer symptoms.
Meaning: Final Preparation
Action: Rapid brain development. More frequent prenatal visits. Preparation for delivery.
Meaning: Ready for Birth
Action: Baby is fully developed. Labor can safely begin anytime. Watch for signs of labor.
Note: Term pregnancy is now defined as 39-40 weeks. Early term is 37-38 weeks, late term is 41 weeks. Induction or C-section before 39 weeks without medical indication is discouraged.
About Due Date Calculator
Formula
EDD = LMP + 280 days (or Conception + 266 days) Naegele's Rule simplified: Add 7 days to LMP date, subtract 3 months, add 1 year. Example: LMP May 1st + 7 days = May 8th, minus 3 months = February 8th, next year = February 8th, 2027.
Current Standards: ACOG (American College of Obstetricians and Gynecologists) considers first-trimester ultrasound the most accurate dating method. Due dates may be adjusted if ultrasound differs from LMP dating by more than 7 days. Full-term pregnancy is 39-40 weeks; delivery before 39 weeks requires medical indication.
Frequently Asked Questions
How accurate is the due date calculation?
Due date calculations from LMP are estimates with significant uncertainty. Only about 5% of babies arrive on their exact due date. About 80% of babies are born within 10 days of the due date (between 38-42 weeks). First-trimester ultrasound is more accurate, typically within 5-7 days. The due date gives healthcare providers a reference point, but expect baby anywhere within a 4-week window around it.
What if my cycles are irregular?
LMP-based calculations assume a 28-day cycle with ovulation on day 14. If your cycles are longer, shorter, or irregular, the calculation will be less accurate. A woman with 35-day cycles ovulates around day 21, making her due date about a week later than LMP calculation suggests. Early ultrasound dating is especially important for irregular cycles since it measures the embryo directly rather than relying on cycle assumptions.
Why might my doctor change my due date?
Doctors adjust due dates when first-trimester ultrasound measurements differ significantly from LMP dating (typically more than 7 days). The ultrasound measures the embryo/fetus directly and is more reliable than calculations based on last period. Later ultrasounds are less accurate for dating because babies grow at different rates after the first trimester. The due date may also be adjusted if you're certain about conception date from fertility treatments.
What happens if I go past my due date?
Going past your due date is common - about 30% of pregnancies go beyond 40 weeks. Providers typically offer increased monitoring after 40 weeks and discuss induction options by 41 weeks. After 42 weeks (post-term), risks increase including decreased amniotic fluid, larger baby size, and placental aging. Most providers recommend delivery by 42 weeks. Being 'overdue' by a few days is normal and not concerning.
How is pregnancy measured - weeks or months?
Healthcare providers use weeks because it's more precise for tracking development and scheduling tests. When people say 'months,' it's roughly weeks divided by 4, but pregnancy months don't align perfectly with calendar months. At 16 weeks, you're 4 months pregnant; at 40 weeks, you've completed 9 calendar months plus about a week. The confusion is why medical professionals stick with weeks.