How it works
Estimate your due date, current pregnancy progress in weeks/days, and trimester from your last period.
Enter the first day of your last period and an optional reference date (defaults to today). The calculator estimates the due date with Naegele's rule and reports how far along the pregnancy is.
Formula
Due date = LMP + 280 days; days pregnant = reference − LMP; weeks = ⌊days ÷ 7⌋. Trimesters: first < 14 weeks, second 14–27, third ≥ 28.
LMP- First day of last menstrual period (date)
asOf- Reference date (date)
Examples
- LMP 1 Jan 2023, as of 1 Jun 2023LMP 2023-01-01 · reference 2023-06-01Due date 2023-10-08 · 151 days · 21 weeks · second trimester
Frequently asked questions
Is this a medical measurement?
No. It is a calendar estimate. A clinician will confirm dating with ultrasound and adjust as needed.
How is this different from the due-date calculator?
The due-date calculator gives the due date; this one also tracks current week, day, and trimester progress.
How to read the result
Pregnancy is commonly dated from the last period; weeks pregnant and trimester are reference points for pregnancy stages.
Limitations
Assumes a 28-day cycle and average timing. Not a substitute for prenatal care or medical advice.
Source: Naegele's rule (LMP + 280 days) with the standard 14/28-week trimester boundaries.