🤰 Pregnancy Week Calculator
Find out how many weeks pregnant you are. Calculate your current pregnancy week and gestational age from your last menstrual period (LMP), ultrasound, conception date, or IVF transfer date. Includes week-by-week fetal development milestones.
How Many Weeks Pregnant Am I?
Your pregnancy week is the number of weeks and days that have passed since the first day of your last menstrual period (LMP). This is called your gestational age and is the standard way healthcare providers date pregnancies.
For example, if it has been 87 days since your LMP, you are 12 weeks and 3 days pregnant (87 ÷ 7 = 12 weeks with 3 days remaining). Your provider may write this as "12w3d".
Because ovulation typically occurs about two weeks after the LMP, your gestational age is usually about 2 weeks ahead of the actual fetal age (time since conception).
Pregnancy Week Calculation Methods
There are several ways to determine your pregnancy week, depending on what information is available:
- Last Menstrual Period (LMP): The most common method. Your due date is calculated as LMP + 280 days (40 weeks). If your cycle is longer or shorter than 28 days, an adjustment is made.
- Ultrasound Dating: An early ultrasound (before 14 weeks) is the most accurate method. The sonographer measures the fetus (crown-rump length in the first trimester, biparietal diameter and head circumference later) to estimate gestational age.
- Conception Date: If the exact date of conception is known, gestational age is calculated from that date plus 266 days (38 weeks) to the due date, then converted to the LMP-based timeline.
- IVF Transfer Date: For IVF pregnancies, gestational age is calculated from the embryo transfer date. A Day 3 transfer adds 263 days to the transfer date, and a Day 5 transfer adds 261 days.
Pregnancy Timeline and Trimesters
Pregnancy is divided into three trimesters:
- First Trimester (Weeks 1–13): The period of major organ development. The highest risk of miscarriage occurs during this time.
- Second Trimester (Weeks 14–27): Often called the "golden period" — nausea typically subsides, energy returns, and fetal movement (quickening) is first felt.
- Third Trimester (Weeks 28–40+): The period of rapid fetal growth and lung maturation. Prenatal visits become more frequent.
Full term is defined by ACOG as 39–40 weeks. The normal range for delivery is 37–42 weeks. Only about 5% of babies are born on their exact due date.
Why Use This Calculator?
- Multiple calculation methods: Supports LMP, ultrasound, conception, and IVF dating.
- Instant results: Get your pregnancy week, trimester, and due date.
- Week grid: See all 40 weeks at a glance with your current week highlighted.
- Milestone timeline: Track key pregnancy milestones and upcoming tests.
- Free & private: No registration, no data storage — all calculations are done in your browser.
❓ Pregnancy Week Calculator FAQ
How many weeks pregnant am I?
Your pregnancy week is the number of weeks since the first day of your last menstrual period (LMP). Enter your LMP above to calculate your current week and day.
What is gestational age?
Gestational age is the age of a pregnancy measured from the first day of the LMP. It is the standard method used by healthcare providers and is usually about 2 weeks ahead of fetal age.
What is the difference between gestational age and fetal age?
Gestational age is measured from the LMP, while fetal age is measured from conception. Gestational age is typically 2 weeks ahead of fetal age.
How accurate is an ultrasound for dating pregnancy?
An early ultrasound (before 14 weeks) is the most accurate method for dating a pregnancy, with an accuracy of ±5–7 days. Later ultrasounds are less accurate for dating.
What if my cycle is not 28 days?
If your cycle is longer or shorter than 28 days, the LMP-based calculation may be adjusted. The calculator above allows you to enter your average cycle length. An early ultrasound is the most reliable way to date the pregnancy.
What is full term?
Full term is defined as 39–40 weeks of gestation. The broader normal range for delivery is 37–42 weeks.
How is an IVF pregnancy dated?
IVF pregnancies are dated from the embryo transfer date. A Day 3 transfer adds 263 days to the transfer date, while a Day 5 transfer adds 261 days. This gives the LMP-equivalent date, from which gestational age is calculated.
What is the viability threshold?
Viability — the point at which a fetus can potentially survive outside the womb — is generally considered to be around 24 weeks of gestation, though this varies by hospital and country.
How accurate is this calculator?
This calculator uses standard pregnancy dating methods (Naegele's rule, ultrasound-based dating, and IVF transfer calculations). However, every pregnancy is unique. Always consult your healthcare provider for personalized advice.
Is this calculator free?
Yes, this calculator is completely free to use. No registration or personal data storage is required.