How We Verify Calculations

Last updated: April 28, 2026

Teachers, students, and parents copy numbers from QuickGrade into real gradebooks and report cards, so every calculator has to match the math a teacher would do by hand. This page describes the formulas we use, the test cases we check against, and how we handle rounding.

The formulas we use

Easy Grader — percentage = (total − wrong) ÷ total × 100. Partial credit is supported by accepting decimal values for wrong answers. Deep dive: how to calculate grades.
Weighted Grade Calculator — Σ(score × weight) ÷ Σ(weight). Weights are normalized when they do not sum to 100%. See weighted grades explained.
Final Grade Calculator — needed = (target − current × (1 − w)) ÷ w, where w is the final exam's weight as a decimal. Deep dive: how to calculate a final grade.
Letter Grade Calculator — percentage bands from the standard US 10-point scale and plus/minus scale published on our grading scale chart.
GPA Calculator — GPA = Σ(gradePoints × credits) ÷ Σ(credits) using the common 4.0 scale. See the GPA guide.

Test cases we check

Every calculator is spot-checked against known worked examples before it ships and after every meaningful code change:

Easy Grader: 20 questions with 3 wrong should return 85%; 25 questions with 0 wrong should return 100%; 30 questions with 30 wrong should return 0%.
Weighted Grade: 90 at 40% + 80 at 60% should return 84.0%.
Final Grade: current 82, target 90, final worth 25% should require 114 on the final (i.e. not achievable — the calculator flags this).
GPA: A (4.0, 3 cr) + B (3.0, 4 cr) + C (2.0, 3 cr) should return 2.95.

Rounding and display

Internal math is done in full precision. Percentages are displayed with optional decimals so that borderline scores (for example 89.5%) do not silently round into a different letter grade. When a school uses a non-standard rounding rule, we recommend checking against the official rubric.

How a change reaches the site

Nothing on this site is edited directly in production. A change to a formula, a grading band, or a worked example goes through the same four steps every time:

Source check. We identify what the change is based on — a published grading scale, a registrar's policy, a standard arithmetic definition, or a reader report with concrete numbers.
Recalculation by hand. The affected cases are worked out on paper first, so the expected answer exists before the code does.
Regression pass. The full set of test cases above is re-run, not just the case that changed. A fix to rounding in one calculator has broken letter-grade boundaries in another before, which is why the whole set runs every time.
Date stamp. The page's last-updated date changes only when the content or math changed, never as a side effect of an unrelated deployment.

Where the grading scales come from

Percentage-to-letter boundaries are not universal, and we do not present them as if they were. The default 10-point scale (90/80/70/60) and the plus/minus variant used across our calculators reflect the most common conventions in US secondary and post-secondary grading. Where a meaningful alternative exists — 7-point scales, no-minus scales, or 4.3-point GPA scales — we document it on the grading scale chart rather than silently picking a winner.

Every calculator that converts a percentage to a letter says which scale it used. If your institution differs, the percentage remains correct and only the letter needs remapping. That separation is deliberate: the arithmetic is objective, the letter is policy.

What we deliberately do not do

We do not guess at rounding. Results are shown with decimals intact so a borderline score is visible rather than resolved for you. See how grade rounding works.
We do not apply curves. Curving is a teacher's decision made after scoring, and no formula can predict it.
We do not store your numbers. Calculations run in your browser; nothing you enter is transmitted or saved.
We do not present output as an official grade. Your school's gradebook is authoritative. Our job is to match the math a teacher would do by hand, and to say plainly when the answer depends on a policy we cannot see.

Known limitations

Some grading situations cannot be reduced to a formula, and our calculators will not attempt them: dropped lowest scores, standards-based reporting that never converts to a percentage, mastery retakes that replace prior attempts, and any grade that is partly a professional judgment. In those cases the guides explain the reasoning and point you back to your own course policy rather than producing a number that looks more certain than it is.

Reporting an issue

Found a case where our output disagrees with a gradebook or a worked textbook example? Please email us through the contact page with the exact inputs — we treat calculator accuracy as the highest-priority issue on the site.