Find your current pregnancy week, trimester and estimated due date from the first day of your last period.
pregnant
How to use this tool
Use the first day of your last menstrual period — this is the standard dating starting point.
Leave it as today, or pick any date to see which week you were (or will be) on that day.
Weeks run from the LMP, not from conception; trimester 1 is weeks 1–13, trimester 2 is 14–27, trimester 3 is 28+.
The due date is LMP + 280 days (40 weeks) — only a minority of births fall exactly on it.
Formula & worked example
LMP 5 January 2026, reference 2 February 2026: 28 days elapsed = 4 weeks, 0 days, trimester 1, estimated due date 12 October 2026.
Limitations — read this before you rely on it
Pregnancy weeks counted from LMP are about two weeks ahead of weeks since conception. Cycle length, irregular cycles and early ultrasound can shift the dates, and only about 5% of babies arrive on their due date. This is general information only, not medical advice — discuss dating and any concerns with your clinician or midwife.
Frequently asked questions
Count from the first day of your last period: divide the days since then by 7. This calculator does that and shows the remaining days too.
Conception day is rarely known exactly, so clinicians date pregnancy from the LMP, which adds roughly two weeks before conception.
Trimester 1: weeks 1–13. Trimester 2: weeks 14–27. Trimester 3: week 28 until birth.
It is an estimate (LMP + 280 days). An early ultrasound usually dates pregnancy more accurately, especially with irregular cycles.
No. It is an estimate for general information. Always follow the advice of your own clinician or midwife.