Gestational Age Calculator
Gestational age is the medical way of dating a pregnancy — it counts weeks from the first day of your last menstrual period (LMP), not from conception. This is why "weeks pregnant" is typically two weeks ahead of the actual fertilisation date.
Enter your LMP and this calculator shows your gestational age today, which trimester you are in, your estimated due date (LMP + 280 days) and your approximate conception window. Doctors, ultrasound reports and maternity records all use gestational age, so it is the number to know.
Medical disclaimer: This tool gives general estimates only and is not medical advice. Always confirm dates, results and any concerns with your doctor or midwife.
Formula
Gestational age = today − LMP (in weeks + days) EDD = LMP + 280 days
Example
LMP = 1 June 2026, today = 15 September 2026. Gestational age = 15 weeks 1 day → second trimester. EDD ≈ 8 March 2027.
How to Use
- 1. Select the first day of your last period.
- 2. Click "Calculate".
- 3. Read your weeks, trimester and due date.
Frequently Asked Questions
How is gestational age calculated?
Weeks and days from the first day of your last menstrual period (LMP).
Why is gestational age ahead of conception?
Pregnancy is dated from LMP; conception typically occurs ~2 weeks later.
What if my cycles are irregular?
LMP dating is less reliable — an early ultrasound gives a better estimate.
Is this medical advice?
No — it is an estimate. Confirm dating with your doctor.