Health & Fitness
Gestational Age Calculator
Gestational Age — gestational Age Calculator counts gestational age in weeks and days from the first day of the last menstrual period (or an adjusted conception date). This page runs that same calculation on your numbers, in your browser: no signup, no uploads, nothing stored.
Gestational Age Calculator lets you track the key dates of a pregnancy in seconds: enter your first day of last menstrual period and as of date for the due date and how far along you are, all worked out locally in your browser.
About this calculator
Gestational Age Calculator counts gestational age in weeks and days from the first day of the last menstrual period (or an adjusted conception date). It matters when you want a quick screening number before deciding whether a habit, plan or measurement deserves a closer look. Here is the calculation on real numbers: If today is 20 weeks and 3 days from the last menstrual period, the pregnancy is at 20w3d — counted in completed weeks plus days. For your own figures, use the calculator above — same method, your inputs, computed on-device.
How to use
- Enter the first day of the last menstrual period (LMP).
- Optionally enter an “as of” date, or leave it blank for today.
- Press Calculate to see gestational age in weeks and days.
- Use ultrasound dating from your provider to confirm.
Why use Gestational Age Calculator
Fast
Calculations run in your browser. No round trip to a server.
Private
Your inputs never leave your device. Nothing is uploaded.
Free
No signup, no paywall, no ads-in-results, no watermarks.
Educational
Uses common calendar-based estimates for educational purposes only. Confirm medical questions with a qualified professional.
Mobile-ready
Optimised for phones, tablets, and desktops alike.
Transparent
Clear about the method used and its limits, with disclaimers where they matter.
Common uses
Use it for planning antenatal appointments
Gestational Age as a general guide between scans
Use it when counting gestational age
Use it for first-time-parent planning
Use it for tracking a pregnancy week by week
Use it when estimating the due date
Technical notes
Gestational Age Calculator counts gestational age in weeks and days from the first day of the last menstrual period (or an adjusted conception date).
These are general-population estimates and not a substitute for advice from a qualified clinician.
The tool works offline once loaded, since every computation is client-side.
FAQ
How is gestational age calculated?
It counts the days from the last menstrual period to the chosen date, then expresses them as completed weeks plus extra days — for example 160 days is 22 weeks and 6 days.
What is the difference between gestational age and fetal age?
Gestational age is measured from the LMP, while fetal (conceptional) age is measured from conception and is about two weeks less.
Why does it warn about unrealistic dates?
If the LMP implies more than about 45 weeks of pregnancy, the dates are likely mistaken, so the tool asks you to re-check rather than show an impossible result.
Does the Gestational Age Calculator send my data to a server?
No. The Gestational Age Calculator runs entirely in your browser — your inputs never leave your device, and nothing is uploaded or stored.
Worked example
If today is 20 weeks and 3 days from the last menstrual period, the pregnancy is at 20w3d — counted in completed weeks plus days.