How to Use the Percentage Calculator
The Tooldit Percentage Calculator combines five common percent calculations into a single tool. Pick the mode that matches the question you're trying to answer using the tabs at the top, then fill in the two number fields. Results update instantly — there's no "Calculate" button to press, and you can try the example chips under each tab to see how each formula behaves.
- X% of Y— find a portion of a number. Use this for sales tax, tips, discounts, allocations and any "take this slice of that total" question.
- X is what % of Y — find what fraction one number is of another. Useful for grades, progress bars, polling shares and budgeting.
- Percentage increase — measure how much a value grew. Useful for raises, price hikes, stock returns and traffic growth.
- Percentage decrease — measure how much a value dropped. Useful for sale prices, weight loss, inventory reductions and depreciation.
- Percentage difference — compare two values when neither is "original". Useful for A/B comparisons, scientific measurements and benchmarking.
Each result card shows the actual formula used with your numbers substituted in, plus a one-sentence interpretation in plain English. Hit the Copy button to grab a clean text summary. Use the keyboard left/right arrows on the tabs to switch modes without leaving the keyboard.
Percentage Formulas Explained
All five modes are built on simple algebra. Here's the formula behind each, with a worked example you can verify in the calculator.
Note that percentage change (modes 3 and 4) is not symmetric: a 50% increase followed by a 50% decrease does not bring you back to the original. That's why percentage difference(mode 5) divides by the average of the two values — it gives the same answer regardless of which value you call "first", which is the right choice when there's no clear baseline.
Common Use Cases
- Sales tax & tips — work out what 8.5% of a restaurant bill is, or add a 18% tip in your head.
- Discounts & sales — figure out the final price when something is 30% off, or check how much you saved.
- Grades & test scores — convert raw points to a percentage (e.g. 47/60 → 78.33%).
- Investment returns — compute the percent return between a buy price and current price.
- Statistics & science — report a symmetric percent difference when comparing two measurements.
- Body weight & fitness — track percent change in weight, body-fat or lift volume.