About this tool
The Pregnancy Week Calculator is a free, in-browser tool that tells you how far along a pregnancy is — gestational age in weeks and days, the current trimester, the estimated due date and the percentage completed. You can start from the last menstrual period (LMP), the conception date, or an IVF embryo transfer date (day-3 or day-5 transfer).
The due date follows Naegele's rule: 280 days (40 weeks) after the LMP. Conception and IVF dates are converted to an LMP-equivalent first (conception ≈ LMP + 14 days; a day-3 transfer ≈ LMP + 17 days; a day-5 transfer ≈ LMP + 19 days), which is the same convention clinicians use. All calculations happen locally in your browser.
This tool is informational only — it is not medical advice.
Frequently asked questions
Why is gestational age counted from the last period?
By medical convention pregnancy is dated from the first day of the LMP, about two weeks before conception, so you are already "2 weeks pregnant" at conception — that is why the calculator converts every input to an LMP-equivalent date.
How do the trimesters split?
This calculator uses the common convention: first trimester through week 13, second trimester weeks 14–27, third trimester from week 28 until birth.
How accurate is the due date?
Naegele's rule (LMP + 280 days) is a population average — only about 1 in 20 babies arrive exactly on it, and an ultrasound-based date from your clinician takes precedence.
Is this medical advice?
No. The dates are informational estimates calculated locally in your browser; always follow the dating and guidance provided by your prenatal care provider.