Pregnancy Weeks Calculator
Find out how far along you are in weeks + days, your estimated due date, trimester, and pregnancy progress.
Note: This tool is for general education and does not replace prenatal care or ultrasound dating from your clinician.
How many weeks are in pregnancy?
A full-term pregnancy is generally considered to be about 40 weeks (280 days), measured from the first day of your last menstrual period (LMP). This can feel confusing because conception usually happens about two weeks after that date. In other words, clinical pregnancy dating starts before fertilization.
This calculator helps you answer common questions like:
- How many weeks pregnant am I today?
- How many days pregnant am I?
- What trimester am I in?
- When is my estimated due date?
How this pregnancy calculator works
Method 1: Last menstrual period (LMP)
This is the most commonly used method in routine pregnancy dating. The calculator counts days from your LMP to your selected “as of” date, then converts that to weeks and days.
If your cycle is longer or shorter than 28 days, the tool adjusts your due date using your cycle length. For example, with a 30-day cycle, ovulation may occur later, which shifts estimated due date by about 2 days.
Method 2: Known due date
If a provider has already given you an estimated due date (EDD), you can enter it directly. The calculator then back-calculates gestational age as of your chosen date.
Understanding your results
After calculating, you will see:
- Gestational age: Example: 18 weeks 4 days.
- Estimated due date (EDD): Based on your selected method.
- Estimated conception date: Approximate and not exact.
- Trimester: First, second, or third trimester.
- Time to due date: Days remaining or overdue days.
Remember that due dates are estimates, not deadlines. Many healthy births happen before or after the exact date.
Trimester guide (quick reference)
- First trimester: 0 weeks to 13 weeks 6 days
- Second trimester: 14 weeks to 27 weeks 6 days
- Third trimester: 28 weeks to birth
Why your due date might change
Even if your calculator gives one result, your provider may refine your dating based on ultrasound, especially early in pregnancy. This is normal and common. Factors that can affect date estimates include:
- Irregular menstrual cycles
- Uncertain LMP date
- Recent hormonal contraception use
- Early ultrasound findings
- Assisted reproductive technology (such as IVF)
Frequently asked questions
Is pregnancy 9 months or 10 months?
Both descriptions are used. Clinically, pregnancy is tracked as 40 weeks (about 9 months plus 1 week). In everyday conversation, people often say 9 months.
How accurate is an online pregnancy week calculator?
It is usually accurate for basic estimation if your dates are correct. However, medical dating from your prenatal provider is the standard for care decisions.
What if my result says I am overdue?
If your date passes 40 weeks, your provider will monitor you and your baby closely and discuss next steps. Always follow your care team’s recommendations.
Important health note
This calculator is educational and not medical advice. If you have pain, bleeding, severe symptoms, reduced fetal movement, or other concerns, contact your obstetric provider promptly or seek urgent care.