Keep Track of Your Growing Baby and Your Pregnancy Milestones
Somewhere between "I just found out I'm pregnant" and "Is it labor day yet?" you'll find yourself constantly wondering: *Exactly how far along am I?* Each week of pregnancy brings new changes to your body and new milestones for your baby. This calculator tells you exactly where you are in your 40-week journey, down to the day.
What This Calculator Does
This calculator takes any date and tells you exactly how many weeks and days pregnant you are (or were on that date). Input your first day of last menstrual period or your due date, and the calculator instantly computes your current gestational age. It also identifies which trimester you're in and provides context about what's happening in your pregnancy at this stage. Whether you're tracking your progress for prenatal appointments, curiosity, or simply because you love having data, this tool keeps you oriented.
How to Use This Calculator
You have two ways to determine your pregnancy timeline. If you know your last menstrual period (LMP) date, enter that, the calculator will count forward from day 1. If you don't remember your LMP but know your due date, enter that instead, and the calculator will count backward (since your due date is 40 weeks from LMP). You can also check your pregnancy progress on any past or future date by adjusting the "today" date.
The result shows:
Use this calculator at your regular prenatal appointments to match what your healthcare provider tells you, or simply track your progress whenever you're curious.
The Formula Behind the Math
Weeks Pregnant = (Today's Date - First Day of Last Period) / 7
Days Remaining = (Today's Date - First Day of Last Period) % 7
Here's how it works: Pregnancy is measured in weeks, starting from day 1 of your last menstrual period. Each week equals 7 days. So if you're 12 weeks and 3 days pregnant, that means 12 complete weeks have passed, plus 3 additional days.
Trimester Breakdown:
Working Example:
Important note: The term "weeks pregnant" always refers to gestational age, measured from the first day of your last period, even though the egg probably wasn't fertilized until about two weeks later. This is why you might hear "You're 2 weeks pregnant" even if you think you just conceived. It's confusing but standard in obstetrics.
Due date math (reverse calculation):
Our calculator does all of this instantly, but now you understand exactly what it's computing.
Your Trimesters: What Happens When
The three trimesters divide your pregnancy into distinct phases, each with its own changes and milestones.
First Trimester (Weeks 1–13): Your baby develops from a fertilized egg to a recognizable human form with a beating heart, fingers, toes, and facial features. You might experience morning sickness, fatigue, and mood changes. Around week 12, you'll likely have your first ultrasound, often called the dating scan or nuchal translucency scan. This is when many parents choose to share their pregnancy news.
Second Trimester (Weeks 14–26): Often called the "golden period," this is when energy returns and you'll start showing noticeably. Your baby grows rapidly and starts moving, which you'll feel as fluttering (called quickening) around week 18–20. You'll typically have a second ultrasound (anatomy scan) around week 20, where you can see your baby's body in detail and learn the sex if you want to. The risk of miscarriage drops significantly after the first trimester.
Third Trimester (Weeks 27–40): Your baby gains most of its weight now, and you'll feel stronger movements and kicks. You'll have more frequent prenatal appointments. Around week 36, your healthcare provider will check your baby's position (head-down is ideal for vaginal delivery). You might experience Braxton-Hicks contractions (practice contractions), swelling, and back pain. Your baby's lungs and brain are finishing development, getting ready for independent life outside the womb.
Why This Matters for Your Prenatal Care
Your healthcare provider bases all recommendations, including testing, monitoring, and delivery timing, on your gestational age. Knowing your exact week helps you understand what tests are due, when to expect certain symptoms, and what your baby's development looks like. It also helps your provider determine if your baby is growing appropriately. If your baby's measurements on ultrasound don't match your gestational age, your due date might be adjusted, this is normal and common, especially in early pregnancy.
Tracking Your Progress and Planning Major Life Events
Many parents use this calculator to coordinate maternity leave, plan their birth center or hospital visits, and schedule important life events around their due date. If you're trying to time a move, finish a work project, or plan a babymoon, knowing exactly how many weeks you have left helps you make informed decisions. Just remember: your due date is an estimate, and your baby may arrive 1–2 weeks earlier or later. Don't make rigid plans tied to a single date.
Tips and Things to Watch Out For
Your due date may shift after early ultrasounds. If your first ultrasound shows your baby is smaller or larger than expected for your LMP date, your due date will be adjusted. Ultrasounds in the first 12 weeks are accurate to within about 3 days. Trust your ultrasound over date calculations.
Gestational age and baby age are different. Gestational age is measured from your last period. "Baby age" or chronological age is typically measured from the birth date. A newborn born at 39 weeks gestation is technically 40 weeks old in medical terms, but zero days old in the real world. This matters for developmental milestones, premature babies are "corrected" to their due date for developmental assessments in the first year.
Irregular cycles mean less accurate dating. If your cycle is very long, very short, or irregular, the calculator's date might be off. Your healthcare provider uses ultrasound to refine the estimate, so this gets corrected.
You can't actually predict the exact due date. While 40 weeks is the average, normal pregnancies range from 37 to 42 weeks. Babies born between 39 and 40 weeks are considered "term" and are generally fully developed.
Preterm birth is before 37 weeks. If you go into labor before week 37, it's considered preterm. Your healthcare provider will monitor you closely if you have any signs of early labor.
This calculator provides general information only. Always consult your OB-GYN, midwife, or pediatrician for medical guidance specific to your pregnancy and baby.
Frequently Asked Questions
When should I start counting weeks pregnant?
Weeks are counted from the first day of your last menstrual period, even though conception typically happens about 2 weeks later. This is the medical standard, so when you enter the office at "12 weeks pregnant," your baby is actually about 10 weeks old biologically. It's confusing but consistent.
Why does my due date keep changing?
Early ultrasounds (before 12 weeks) are accurate to within a few days. If your baby measures bigger or smaller than your LMP suggests, your due date will be adjusted. Later ultrasounds are less accurate for dating, so adjustments typically stop after the first trimester.
What's the difference between due date and EDD?
EDD (estimated due date) is the formal term for your due date. They mean the same thing, it's the estimated date your baby will arrive, calculated as 40 weeks from LMP.
Can I deliver before 37 weeks?
Labor before 37 weeks is considered preterm. Your healthcare provider will monitor you and may recommend interventions to delay delivery if preterm labor seems likely, giving your baby more time to develop.
Am I fully term at 37 weeks?
Babies born at 37 weeks are technically "early term," but they're generally considered viable and ready for life outside the womb. Full term is 39–40 weeks. Your provider will counsel you about the small differences in outcomes if delivery is planned early.
How long can I stay pregnant past my due date?
Most providers allow pregnancy to continue until 41–42 weeks, assuming both you and your baby are healthy. If you go past that, your provider will discuss induction to reduce risks. Discuss your preferences with your healthcare provider in advance.
Related Calculators
Once you know your current week, try our Due Date Calculator to verify or adjust your due date. If you're curious about when you likely conceived, use our Conception Date Calculator. As you progress, our Baby Growth Percentile Calculator will help you track whether your baby is growing well for your stage of pregnancy.