Pregnancy Calculator – How Many Weeks Pregnant Am I?
Pick a starting date — last period, conception, or due date — to see your current week, trimester, and estimated due date.
“How many weeks pregnant am I?” is one of the first questions after a positive test. This pregnancy calculator estimates gestational age from your last period, conception date, or a known due date — and shows trimester, estimated due date, and days remaining.
Dating follows Naegele’s rule: estimated due date = first day of last period (LMP) + 280 days (40 weeks). From a conception date, due date ≈ conception + 266 days. From a known due date, gestational age is counted backward from that date. Trimesters use weeks 1–13, 14–27, and 28+.
Ultrasound or IVF dating from your provider may differ — follow their schedule for care. For BMI screening, see the BMI Calculator. Dates stay in your browser.
How to use
- Choose how you want to date the pregnancy: first day of last period (LMP), conception date, or known due date.
- Enter that date.
- Read current week + day, trimester, estimated due date, and days remaining.
- The progress bar shows how far along a typical 40-week pregnancy is. Use Reset to clear.
Tips
- Most clinicians date pregnancy from the first day of the last menstrual period (LMP), not conception — that is why “week 4” can mean you conceived about two weeks earlier.
- Naegele’s rule estimates due date as LMP + 280 days (40 weeks). Your provider may adjust this with ultrasound.
- Trimesters here: 1st through 13 weeks 6 days, 2nd through 27 weeks 6 days, 3rd from 28 weeks onward.
- This tool is for planning and curiosity — not a substitute for prenatal care or medical advice.
FAQ
How many weeks pregnant am I?
Pregnancy is usually counted from the first day of your last period. Enter that date (or conception/due date) and the calculator shows completed weeks and extra days as of today.
What is Naegele’s rule?
A common due-date estimate: add 280 days (40 weeks) to the first day of the last menstrual period. Equivalently, LMP − 3 months + 1 year + 7 days for a typical cycle. This calculator uses LMP + 280 days.
What if I know my conception date instead?
Conception is typically about 14 days after LMP in a 28-day cycle. The calculator treats conception as gestational day 14, so due date ≈ conception + 266 days (38 weeks).
What if I already have a due date?
Enter the due date and choose “Due date.” The calculator works backward (due date − 280 days) to estimate LMP-based gestational age and current week.
Which trimester am I in?
First trimester through 13 weeks 6 days, second through 27 weeks 6 days, third from 28 weeks onward. Exact boundaries can vary slightly by source; these are the cutoffs used here.
Why might my doctor’s dates differ?
Ultrasound dating, irregular cycles, or IVF dating can shift the estimated due date. Always follow your clinician’s dating for medical decisions.