Pregnancy Week Calculator by LMP
Pregnancy Week Calculator by LMP
This calculator estimates your current pregnancy week, trimester, due date, conception date, ovulation date, days remaining, and baby development from the first day of your last menstrual period. It uses standard obstetric dating so you can understand what is happening this week without needing to guess.
Calculate your pregnancy
Enter the first day of your LMP to estimate your journey.
Your current pregnancy snapshot
These numbers update instantly as you adjust the inputs.
Pregnancy timeline
Key landmarks from early pregnancy to full term.
Baby development this week
Changes in your body
This week’s checklist
Upcoming milestones
Pregnancy calendar
A simple view of your current week, trimester, due date, and upcoming appointments.
How pregnancy weeks are calculated
Plain-language information for your next step.
Why doctors use LMP
Doctors usually estimate pregnancy from the first day of the last menstrual period because it is a clear date that is often known even before a pregnancy test. This method is standard in obstetric care and helps guide prenatal appointments, screening tests, and fetal growth checks.
Understanding gestational age
Gestational age counts from the first day of the last menstrual period, not from the day of conception. That is why a pregnancy is often described as “six weeks pregnant” even before the embryo has reached the sixth week of development.
How accurate is this calculator?
This tool gives a careful estimate for planning and education. Ultrasound measurements can adjust the estimate, especially if your cycle is irregular or if your dates are uncertain. If you are using assisted reproduction, your care team may calculate dates differently.
Pregnancy by trimester
The first trimester runs through week 13, the second trimester through week 27, and the third trimester continues to delivery. Each stage brings different changes, growth patterns, and prenatal care needs.
Frequently asked questions
Helpful answers for common questions about pregnancy dating.
Does this calculator replace a doctor’s estimate?
No. It gives an evidence-based estimate for educational use. Your clinician may refine it using ultrasound or your medical history.
What if my cycle is not 28 days?
The calculator lets you enter your average cycle length so ovulation and conception estimates can be adjusted.
Why is my due date an estimate?
Only about 5% of births happen exactly on the estimated due date. Most deliveries happen within a week or two of it.
