Gestational Age Calculator - LMP Pregnancy Tracker

Track your gestational age and estimate your official baby due date based on your Last Menstrual Period (LMP) or conception date.

First Day of Last Period (LMP)

Average Cycle Length (days)

Enter your LMP and tap Calculate.

How the LMP Method Works

Gestational age counts from the first day of your Last Menstrual Period, which is roughly two weeks before conception. Doctors use LMP because it's a date women reliably remember, and it produces a consistent starting point across every pregnancy.

The classic Naegele's rule adds 280 days (40 weeks) to LMP to produce the Estimated Due Date (EDD). Our calculator refines that: if your cycle is longer than 28 days, ovulation happens later, so we shift EDD forward by the same difference. Only about 5% of babies actually arrive on their EDD — the normal window is 37 to 42 weeks.

Trimester milestones

First trimester (1–13 weeks) — organ development, highest miscarriage risk, first ultrasound.
Second trimester (14–27 weeks) — anatomy scan around week 20, first fetal movements.
Third trimester (28+ weeks) — rapid weight gain, glucose screening, birth planning.

After delivery, track your baby's growth with the main Age Calculator hub or compare mother-and-baby health markers using our Biological & Health Age tool.

Frequently Asked Questions

How is gestational age calculated from LMP?+

Gestational age counts from the first day of your Last Menstrual Period (LMP), not the day of conception. The number of days elapsed since LMP is divided by 7 to give completed weeks plus remaining days.

How accurate is the Estimated Due Date (EDD)?+

The Naegele-rule EDD (LMP + 280 days) is accurate to within about ±5 days for people with regular 28-day cycles. Longer or shorter cycles shift the date; this calculator adjusts EDD for your average cycle length.

When does each trimester start?+

First trimester: weeks 1–13. Second trimester: weeks 14–27. Third trimester: weeks 28 to delivery. A full-term pregnancy is 37–42 weeks.

What if I don't remember my LMP?+

Book a dating ultrasound. A first-trimester scan measures crown-rump length and gives a gestational age accurate to within ±3–5 days, which is more reliable than LMP recall.