Pregnancy Calculator
Find your due date, current pregnancy week, and trimester from your last menstrual period.
How this is calculated
Due date = LMP + 280 days (Naegele's rule). Conception ≈ LMP + 14 days (ovulation).
Frequently Asked Questions About Pregnancy Calculator
A pregnancy calculator determines your estimated due date, current week of pregnancy, and trimester based on your last menstrual period (LMP). It also estimates your conception date.
How is the due date calculated?
Due date is calculated using Naegele's rule: your last menstrual period date plus 280 days (40 weeks). This assumes a standard 28-day cycle. If your cycle is different, your due date may shift. Ultrasound dating in the first trimester is more accurate.
Is my due date accurate?
Only about 5% of babies are born on their actual due date. Most babies arrive within 2 weeks before or after the due date. First-trimester ultrasound can refine the estimate. Your doctor will confirm your due date at your first prenatal visit.
What are the three trimesters?
First trimester: weeks 1-13 (early development). Second trimester: weeks 14-27 (rapid growth). Third trimester: weeks 28-40 (final growth and preparation). Each has different milestones and screening tests.
What if I don't remember my last period date?
If you can't recall your LMP, your doctor can estimate based on ultrasound measurements, typically done at your first prenatal appointment. First-trimester ultrasound is accurate to within 3-5 days.
Can I use this calculator if my cycles are irregular?
This calculator uses a standard 28-day cycle. If your cycles are irregular, the due date may be off. Ultrasound dating is more reliable for you. Discuss your cycle length with your doctor for a more accurate estimate.
When should I take a pregnancy test?
Most pregnancy tests are reliable after a missed period. For earliest detection, use sensitive tests starting 8-10 days after ovulation (typically around 5 days before missed period). Blood tests can detect pregnancy 6-8 days after ovulation.