Who is behind GradeDuck
I’m Matias Mardones, and I build and maintain GradeDuck from Chile. I make games and web tools, and I started this site because most grade calculators I found gave a number without saying how they got it. When a result disagrees with your school portal, that leaves you guessing.
I’m not a teacher or a school official. What I can do is write calculators carefully, document every rule they use, and test them against worked examples. That is what this site tries to do well.
How the calculators are checked
- Every formula is written out on its page, with at least one example you can redo by hand.
- The grade scale is the standard plus/minus 4.0 scale used by most U.S. schools, and each page says where schools commonly differ.
- The calculations are covered by automated tests built from those worked examples, so a change that breaks the math is caught before it is published.
The full set of rules is on the How we calculate page. If you find a result that looks wrong, please tell me with the numbers you used. Confirmed errors are fixed, and the date on the How we calculate page changes when they are.
How a new calculator gets made
Every tool on GradeDuck goes through the same steps before it’s published:
- Find the official rule. The formula or scale comes from a primary source: a registrar or catalog page, a College Board exam page, or a federal regulation, or the published rules of UC, LSAC, the AAMC or ACT. If a rule varies by school, the page says so and, where it can, lets you enter your school’s own numbers.
- Work examples by hand. Each page has at least one worked example with real-looking numbers, and those same examples become automated tests.
- Link the sources. Guides cite the organization and year behind every figure and link to the page it came from, so you can check it.
- Say what it can’t do. Every calculator has a section on when your school’s number may differ, and estimates (like AP 1–5 scores) are labeled as estimates.
What GradeDuck is not
GradeDuck isn’t a school, a counselor or an admissions service, and it isn’t affiliated with, or endorsed by, the College Board, ACT Education Corp., the Law School Admission Council (LSAC), the Association of American Medical Colleges (AAMC), the University of California or any other school or organization mentioned on the site. Your registrar’s numbers are the official ones; these tools are for checking them and planning ahead.
Your data
The calculators run entirely in your browser. Grades you type are never sent to GradeDuck; they are stored only on your device so they are still there next time. The privacy policy has the details.
How GradeDuck is funded
The site is free to use and is supported by ads. Ads never change how a calculator works or what result it shows, and they are kept away from the calculators themselves.