How is gestational age calculated?

Gestational age is counted from the first day of your last menstrual period (LMP). The number of days since the LMP is shown as weeks plus days, and the estimated due date is the LMP plus 280 days (40 weeks), following Naegele's rule.

How accurate is this tracker?

It uses Naegele's rule, the standard method for an estimated due date, which assumes a regular 28-day cycle. Real cycles vary, and an early dating ultrasound is more accurate. Treat this as an informational estimate, not medical advice — always follow your clinician's dating.

Is my pregnancy data kept private?

Yes. The dates you enter are processed entirely in your browser using JavaScript. Nothing is stored, logged or transmitted anywhere.

Pregnancy Week Tracker

Pregnancy week tracker

Find out how many weeks pregnant you are, which trimester you are in and your estimated due date — all from a single date.

Enter the first day of your last menstrual period (LMP) and the tracker counts forward to today to give your gestational age in weeks and days. If you already have a due date, switch the mode and it works backwards instead.

The calculation follows Naegele’s rule: your estimated due date is your LMP plus 280 days (40 weeks). Trimesters follow the usual convention — first trimester weeks 0–13, second 14–27, third from week 28.

This is an informational estimate, not medical advice. Your clinician’s dating scan always takes precedence. Every date is calculated locally in your browser and nothing is uploaded.