Pregnancy Week Calculator
Find out how far along you are in your pregnancy. Enter your last period date to see your current week, trimester, due date, and baby size. Completely private — runs in your browser.
How the Pregnancy Week Calculator Works
Pregnancy is counted from the first day of your last menstrual period (LMP), not from conception. A full-term pregnancy is 40 weeks (280 days). This pregnancy week calculator determines your current week, trimester, estimated due date, and shows baby development milestones for your stage.
Pregnancy Timeline
1st Trimester: Weeks 1-12 (development begins)
2nd Trimester: Weeks 13-26 (quickening, growth)
3rd Trimester: Weeks 27-40 (final development)
Due Date = LMP + 280 days (Naegele's Rule)
Understanding Pregnancy Weeks
Pregnancy weeks can be confusing because counting starts from your last period, about 2 weeks before conception. So when you are "4 weeks pregnant," the embryo is actually about 2 weeks old. This standard counting method (gestational age) is used by doctors worldwide.
Baby Development by Trimester
In the first trimester, all major organs begin forming. The heart starts beating around week 6. By the second trimester, the baby can move, hear sounds, and you may feel kicks. The third trimester is about growth and lung development. By week 37, the baby is considered full-term.
Tips for Getting Accurate Results
For the most accurate results, use up-to-date numbers from official sources. Double-check your inputs before calculating — small errors in the starting values can lead to significantly different outputs. If you are comparing scenarios, keep all variables the same except the one you are testing. Save or screenshot your results for future reference. This calculator uses standard formulas and is designed to give you a reliable quick estimate, though professional advice may be needed for complex situations.
Who Uses Pregnancy Week Calculator
This tool is used by anyone who needs a quick, reliable way to get results without downloading software or creating accounts. Students, professionals, hobbyists, and curious minds all benefit from having instant access to specialized tools in their browser. The privacy-first approach — where no data leaves your device — makes it suitable for sensitive information. Bookmark this page and return whenever you need it.
Frequently Asked Questions
How are pregnancy weeks calculated?
Pregnancy weeks are counted from the first day of your last menstrual period (LMP). This means "Week 1" starts before conception. Actual fertilization usually occurs around Week 2. This is standard medical practice worldwide.
How accurate is the due date?
The due date is an estimate — only about 5% of babies arrive on their exact due date. Most full-term births occur between weeks 37 and 42. Your doctor may adjust the due date based on ultrasound measurements.
What trimester am I in?
1st trimester: weeks 1-12, 2nd trimester: weeks 13-26, 3rd trimester: weeks 27-40. Each trimester brings different developmental milestones and symptoms.
When will I feel the baby kick?
Most first-time mothers feel movement (quickening) between weeks 18-25. Experienced mothers may feel it as early as week 16. Early movements feel like fluttering or bubbles.
Is my data private?
Yes. All calculations run entirely in your browser. No pregnancy data is sent to any server. Your health information is completely private.