Pregnancy Due Date Calculator
Enter the first day of your last menstrual period (LMP) and the calculator estimates your due date using Naegele's rule — LMP plus 280 days (40 weeks). It also shows your current week and day of pregnancy, which trimester you are in, and the estimated conception date.
A timeline of key milestones maps out important dates across all three trimesters: first heartbeat, NIPT screening, anatomy scan, viability milestone, glucose test, full term, and more. Each milestone shows the calendar date and whether it has already passed.
Naegele's rule assumes a 28-day cycle with ovulation on day 14. If your cycle is significantly longer or shorter, your actual due date may differ. Only about 5% of babies are born on their exact due date — most arrive within two weeks before or after. This tool is for informational purposes only and is not a substitute for prenatal care.
By The Paper Room Editorial Team — Calculator Tools
Frequently asked questions
What is Naegele's rule?▼
Naegele's rule estimates the due date by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP). It assumes a 28-day menstrual cycle with ovulation occurring on day 14. The rule was named after German obstetrician Franz Naegele and has been used since the early 19th century.
How accurate is the estimated due date?▼
Only about 5% of babies are born on their exact estimated due date. Most births occur within two weeks before or after the due date, which is why doctors consider 37-42 weeks 'term.' A first-trimester ultrasound is more accurate than LMP-based calculation, especially if your cycle is irregular.
What are the trimesters of pregnancy?▼
The first trimester is weeks 1-12, covering major organ development. The second trimester is weeks 13-26, when the baby grows rapidly and movement becomes noticeable. The third trimester is weeks 27-40, when the baby gains weight and prepares for birth. Each trimester lasts roughly 13 weeks.
What is the anatomy scan?▼
The anatomy scan (also called the mid-pregnancy ultrasound or 20-week scan) is typically performed between weeks 18-22. It checks the baby's organs, limbs, spine, and brain for normal development, measures growth, checks the placenta and amniotic fluid, and can reveal the baby's sex if desired.
When is a pregnancy considered full term?▼
A pregnancy is considered early term at 37-38 weeks, full term at 39-40 weeks, late term at 41 weeks, and post-term at 42+ weeks. The American College of Obstetricians and Gynecologists discourages elective delivery before 39 weeks unless medically indicated.