Health & Fitness
Gestational Age Calculator
Gestational Age Calculator is a browser-based calculator tool on CalcToolsBase. Estimate gestational age in weeks and days from the last menstrual period, with the estimated due date. To use it, enter your values and view the result directly in your browser — no signup and nothing to install.
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
The Gestational Age Calculator gives you a quick way to track the key dates of a pregnancy. Enter your first day of last menstrual period and as of date; it then returns the due date and how far along you are, worked out with standard 280-day dating the moment you calculate. It runs fully in the browser, so it is private by design and works offline once loaded.
LMP-based dating is approximate and assumes regular cycles. Early ultrasound dating is the clinical standard, so use this as a quick reference rather than a medical record.
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
Gestational Age for planning antenatal appointments
Gestational Age as a general guide between scans
Gestational Age when counting gestational age
Gestational Age for first-time-parent planning
Gestational Age for tracking a pregnancy week by week
Gestational Age 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.