Pregnancy Week Calculator
Calculate your current pregnancy week, trimester, due date, conception date, and baby size comparison using LMP or due date. Free online pregnancy tracker.
About This Calculator
Our Pregnancy Week Calculator helps expectant parents track their pregnancy progress week by week. Enter your last menstrual period (LMP) date or your estimated due date, along with your average menstrual cycle length, to instantly calculate your current pregnancy week, trimester, due date, conception date, weeks remaining, and what fruit or vegetable size your baby is this week.
The calculator uses Naegele's rule, the standard medical method for estimating due dates. This rule adds 280 days (40 weeks) to the first day of your last menstrual period, assuming a 28-day cycle. If your cycle is longer or shorter, the calculator automatically adjusts the due date by the difference. You can also calculate backwards from a known due date to determine your LMP, conception date, and current week. The conception date is estimated as 14 days after LMP, which is the typical ovulation window.
Pregnancy is divided into three trimesters. The first trimester (weeks 1-13) covers conception and early organ development. The second trimester (weeks 14-26) is when the fetus grows rapidly and movement is felt. The third trimester (weeks 27-40) involves final growth and preparation for birth. A full-term pregnancy ranges from 37 to 42 weeks, with only about 4% of babies born exactly on their calculated due date.
Regional Notes
India: Indian healthcare providers use the same LMP + 280 days method for due date estimation. The first prenatal visit typically occurs around 8-12 weeks for dating scans and confirmation of pregnancy.
US: The American College of Obstetricians and Gynecologists (ACOG) recommends ultrasound dating in the first trimester for the most accurate gestational age assessment. Due dates may be adjusted based on early ultrasound measurements.
UK: The NHS follows NICE guidelines using LMP for dating pregnancies with regular 28-day cycles, and recommends a dating ultrasound between 10 and 14 weeks for confirmation.
Frequently Asked Questions
How is the due date calculated?
The due date is calculated by adding 280 days (40 weeks) from the first day of your last menstrual period (LMP), adjusted for your average cycle length. This is known as Naegele's rule.
How many weeks is a full-term pregnancy?
A full-term pregnancy lasts between 37 and 42 weeks, with 40 weeks (280 days) from the first day of your LMP being the most commonly cited due date. Babies born before 37 weeks are considered premature.
What are the three trimesters of pregnancy?
The first trimester is weeks 1 to 13, the second trimester is weeks 14 to 26, and the third trimester is weeks 27 to 40. Each trimester marks different stages of fetal development and maternal changes.
Can I calculate my due date from my conception date?
Yes. If you know your exact conception date, you can calculate the due date by adding 266 days (38 weeks) to that date. Conception typically occurs around 14 days after the first day of your LMP.
How does menstrual cycle length affect the due date?
Naegele's rule assumes a 28-day cycle. If your cycle is longer or shorter, the due date is adjusted by the difference. For example, a 30-day cycle adds 2 days to the 280-day calculation.
What fruit or vegetable size is my baby this week?
Our calculator compares your baby's size to common fruits and vegetables for each week of pregnancy, from a poppy seed at week 1 to a watermelon at week 40. This helps visualize fetal growth at each stage.
Is the due date calculation the same in India, the US, and the UK?
Yes. Naegele's rule using LMP + 280 days is the standard method worldwide, including India, the US, and the UK. Healthcare providers in all three countries use the same formula to estimate due dates.