# Percentage Calculator Five everyday percentage questions, answered live as you type — a share of a number, a ratio as a percent, percentage change, and increase or decrease. No formulas to remember. Runs in your browser. ## The formulas, in plain terms "Percent" means *per hundred*, so a percentage is just a fraction with 100 on the bottom — 15% is `15/100 = 0.15`. Every calculation here is one of four moves: ### Share of a number **X% of Y = (X ÷ 100) × Y.** 15% of 200 is `0.15 × 200 = 30`. This is the one behind tips, taxes, and discounts. ### Ratio as a percent **X is (X ÷ Y) × 100 percent of Y.** 45 out of 180 is `45/180 × 100 = 25%` — test scores, completion rates, market share. ### Percentage change **Change = ((new − old) ÷ old) × 100.** From 80 to 100 is `(20/80) × 100 = +25%`. Note it's asymmetric: a +25% rise then a −25% fall does *not* return you to the start, because the base changed. ### Increase & decrease **Y ± X% = Y × (1 ± X/100).** 50 increased by 20% is `50 × 1.2 = 60`; decreased by 20% is `50 × 0.8 = 40`. ### Privacy Nothing you type is sent anywhere — the arithmetic runs on your device. --- *Source: [ocxly.com/percentage-calculator.html](https://ocxly.com/percentage-calculator.html) — OCXLY, free 100% client-side privacy-first tools. Free percentage calculator: what is X% of Y, X is what percent of Y, percentage change, and increase or decrease — all computed live. Runs entirely in your browser.*