Pregnancy Week Calculator 2025
Find out exactly how many weeks and days pregnant you are right now from your last menstrual period (LMP) or due date. See your current trimester, your baby's size this week, and your estimated due date.
How Many Weeks Pregnant Am I?
Your pregnancy is measured in weeks counted from the first day of your last menstrual period (LMP) — not from the day you conceived. This is the system every doctor, midwife, and ultrasound scan uses. To work it out, count the number of days from your LMP to today and divide by 7. For example, 24 weeks and 3 days means it has been 171 days since your last period began.
Why Pregnancy Starts Before Conception
It sounds strange, but on the standard pregnancy calendar you are already "2 weeks pregnant" on the day you conceive. That is because the count starts at your LMP, and ovulation (when conception happens) is roughly 14 days later in a typical 28-day cycle. This is why a 40-week pregnancy actually involves about 38 weeks of fetal development.
Weeks, Months & Trimesters
Pregnancy weeks don't divide evenly into calendar months, which is why "how many months" can be confusing. A useful guide:
First Trimester: Weeks 1-13 (roughly months 1-3)
Second Trimester: Weeks 14-27 (roughly months 4-6)
Third Trimester: Weeks 28-40 (roughly months 7-9)
Each trimester is about 13-14 weeks long.
How Accurate Is This Calculator?
This tool uses Naegele's rule (LMP + 280 days) and assumes a regular 28-day cycle. You can adjust the cycle length field if yours is longer or shorter, and the calculator will fine-tune your dates. If you conceived through IVF or have irregular cycles, your clinic's dating will be more precise. A first-trimester ultrasound is the most accurate way to confirm how many weeks pregnant you are, usually within 3-5 days.
What "Viability" and "Full-Term" Mean
Viability is around week 24, when a baby has a chance of surviving outside the womb with intensive medical care. Full-term is weeks 37-42, when the baby is fully developed. Babies born before week 37 are preterm, and pregnancies past 42 weeks are post-term, when doctors often recommend inducing labor.
Frequently Asked Questions
Your weeks pregnant are counted from the first day of your last menstrual period (LMP), not from conception. Count the number of days from your LMP to today and divide by 7. For example, 168 days after your LMP means you are exactly 24 weeks pregnant. Pregnancy is considered full-term at 40 weeks. Enter your dates above to get your exact weeks and days instantly.
Doctors date pregnancy from the first day of your last period because it's a reliable, easy-to-remember marker. Conception (ovulation) usually happens about 14 days later. So at the moment you conceive, you're already counted as "2 weeks pregnant" on the standard calendar. This is why 40 weeks of pregnancy equals about 38 weeks of actual baby development.
This calculator uses the standard 280-day (40-week) pregnancy length (Naegele's rule). It's accurate if you know your LMP and have regular 28-day cycles. You can adjust the cycle-length field to match your body. If your cycles are irregular or you conceived via IVF, your clinic's dates will be more precise. A first-trimester ultrasound is the most accurate dating method (within 3-5 days).
The first trimester is weeks 1-13, the second trimester is weeks 14-27, and the third trimester is weeks 28-40. Enter your dates above and the calculator tells you exactly which trimester you're in right now, plus how many weeks remain until your due date.
Yes. If you already know your estimated due date, choose "Estimated Due Date" above and the calculator works backward. Since a due date is 280 days after your LMP, it subtracts the days remaining until your due date from 280 to find exactly how many weeks and days pregnant you are today.
This calculator shows a friendly fruit or vegetable comparison for your current week, along with the approximate length and weight. For example, at week 12 your baby is about the size of a lime (5 cm), and by week 24 it's about an ear of corn (30 cm). These are averages — every baby grows at its own pace.