Pregnancy Calculator
Free pregnancy due date calculator to estimate your due date, current week, trimester, and conception date. Based on last menstrual period and cycle length with timeline chart.
About This Calculator
The Pregnancy Calculator estimates your due date, current gestational age, trimester, and conception date based on the first day of your last menstrual period (LMP) and your average cycle length. This tool is designed for expectant parents, healthcare providers, and anyone tracking a pregnancy journey. By entering your LMP date and cycle length, you get an instant pregnancy timeline from conception to due date.
The calculation uses Naegele's rule, which adds 280 days (40 weeks) from LMP, with an adjustment for cycle length. For a standard 28-day cycle, ovulation occurs on day 14 and the due date is exactly 280 days after LMP. For longer or shorter cycles, the due date shifts by the difference in days. Conception is estimated at approximately 14 days before the next expected period. The current week and day are calculated by comparing today's date to the LMP date, and trimesters are divided at weeks 13 and 27.
Regional notes: In India, pregnancy care follows guidelines from the Federation of Obstetric and Gynaecological Societies of India (FOGSI) with standard 40-week dating. In the US, the American College of Obstetricians and Gynecologists (ACOG) recommends first-trimester ultrasound for accurate dating. In the UK, the National Institute for Health and Care Excellence (NICE) guidelines suggest early dating scans between 10-14 weeks. While Naegele's rule is universally used, ultrasound-based dating is more accurate, especially for irregular cycles.
Frequently Asked Questions
How is my due date calculated?
Due date is calculated by adding 280 days (40 weeks) from the first day of your last menstrual period (LMP), adjusted for cycle length. This is known as Naegele's rule. Only about 5% of babies arrive exactly on their due date; most come within 2 weeks before or after.
How accurate is LMP-based due date?
LMP-based due dates have a margin of error of 1-2 weeks, especially for women with irregular cycles. Early ultrasound (first trimester) is more accurate. If your cycle length differs from 28 days, adjusting the due date improves accuracy.
What are the trimesters of pregnancy?
First trimester: Week 0-12 (conception to end of 12th week). Second trimester: Week 13-26 (often the easiest period). Third trimester: Week 27-40 (baby grows rapidly, preparing for birth). Each trimester has distinct developmental milestones.
When does conception occur?
Conception typically occurs about 14 days before your expected next period. For a 28-day cycle, this is around day 14. Sperm can survive 3-5 days in the female reproductive tract, so intercourse in the 6-day fertile window can lead to conception.
How long is a normal pregnancy?
A full-term pregnancy lasts between 37 and 42 weeks (259 to 294 days). Babies born before 37 weeks are considered premature. Only about 4% of babies are born exactly on the calculated due date, and 80% arrive within 2 weeks before or after.
What is the conception date method for due date?
If you know the exact date of conception, add 266 days (38 weeks) to calculate the due date. This method can be more accurate if you track ovulation. Conception typically occurs within 24 hours of ovulation, and sperm can survive up to 5 days in the reproductive tract.
How does cycle length affect due date?
For cycles longer than 28 days, ovulation occurs later, so the due date is adjusted by adding the difference. For shorter cycles, the due date is moved earlier. For example, a 30-day cycle adds 2 days to the 280-day calculation. Irregular cycles reduce LMP-based accuracy.
What prenatal tests are done in each trimester?
First trimester: blood tests, urine tests, ultrasound for dating, and NIPT screening. Second trimester: anatomy scan (18-22 weeks), glucose tolerance test, and quad screen. Third trimester: Group B strep test, growth ultrasound, and non-stress test. Schedule varies by country and provider.