How to Calculate Percentages Online (Of, Reverse & Change)

Percentage math shows up in discounts, grades, analytics dashboards, and tip estimates. A clear percentage calculator removes mental-math mistakes when you need “X% of Y”, the reverse whole, or percent change between two values.

Three modes you will use constantly

1. Percent of: what is 18% of 250?
2. Reverse: 45 is what percent of 180? — or 45 is 25% of what?
3. Change: revenue went from 1,200 to 1,500 — what percent increase?

Open Percentage Calculator, pick the mode that matches your question, enter the values, and read the result. Shareable URL presets help teammates repeat the same calculation.

Worked examples

• 18% of 250 → 45 (common tax or tip style math).
• Sale price 80 after 20% off → original was 100 (reverse).
• Users 800 → 1,000 is a 25% increase (percent change).

Related pricing tools

For shelf discounts with tax, use Discount Calculator. For tip splits, use Tip Calculator. For margin vs markup, start with Profit Margin Calculator or the Calculator Kit.

Tip: when a brief says “up 10%”, confirm whether they mean percent of the old value (percent change) or percentage points of a rate.