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About this tool
Common percentage calculations.
The Grade Percentage Calculator works out what a given percentage of a number comes to — (percent ÷ 100) × value — and at the same time shows that value increased and decreased by the same amount. Enter 15 and 200 and it returns 30, along with 230 and 170, so a weighting, a bonus and a deduction are all visible in one result. It is aimed at students and teachers converting mark weightings, grace marks and score adjustments without setting up a spreadsheet.
Open Grade Percentage Calculator on AltFTool — it loads instantly in your browser.
Enter the percentage value you want to calculate in the 'Percent (%)' field, such as 25 for 25%; it starts at 15.
Input the total or base value from which the percentage will be calculated in the 'Of value' field, which starts at 200.
The answer updates as you type, with no button to press: the headline figure is the percentage of that value, captioned 15% of 200 for the defaults, above two cards labelled 'Value + %' and 'Value − %' that add and subtract the result from the base.
The percentage amount, the value plus that amount and the value minus it appear together, so mark-ups and mark-downs need no second calculation.
Change either the percentage or the base number and every figure updates immediately, which makes comparing weightings fast.
Results are grouped with thousands separators and capped at two decimals, so a five-figure total stays legible instead of running together.
Divide the percentage by 100 and multiply by the number: 15% of 200 is (15 ÷ 100) × 200 = 30. That is exactly the arithmetic this tool runs, and it also reports 200 + 30 = 230 and 200 − 30 = 170.
Divide the marks you scored by the total marks and multiply by 100 — 68 out of 80 is (68 ÷ 80) × 100 = 85%. This tool does the reverse operation, taking a percentage and a total and returning the marks, so use it when you know the weighting and want the mark value.
A percentage change is relative to the starting value, a percentage point is an absolute difference. A grade moving from 60% to 63% has risen 3 percentage points but only 5% in relative terms, because 3 ÷ 60 = 5%. Mixing the two is the most common error in grade discussions.
Yes — that is what the two extra rows are for. Entering the percentage and the base value gives you the adjusted totals directly, so a 10% late penalty on a 45-mark submission shows both the 4.5 deduction and the 40.5 result without a second entry.
Add the Grade Percentage Calculator widget to your blog or website — free, responsive, no signup. Just keep the “Widget by AltFTool” credit link visible.
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