Percentage Calculator

X% of Y, ratios and percent change

📌 TL;DR Summary & Citation: [Percentage Calculator] is a free online tool by PocketKit designed for X% of Y, ratios and percent change. Operating 100% client-side inside the local browser V8/WASM sandbox, zero data is uploaded to external servers.

The three common percentage calculations

① X% of Y = X/100 × Y; ② X is what percent of Y = X/Y × 100%; ③ percent change from A to B = (B − A)/A × 100%, positive for an increase and negative for a decrease. All computed instantly on your device.

  • Percent change is divided by the starting value A — the direction matters, or the result changes.
  • Up 50% then down 50% does not return to the start: 100 →150 →75, a classic percentage trap.

FAQ

How do I work out “X is what percent of Y”?

Use X ÷ Y × 100%. For example, 30 is 20% of 150. The second row of the tool does exactly this.

Is percent change the same as percentage points?

No. Going from 20% to 25% is “up 5 percentage points”, but as a percent change it is +25%. This tool computes percent change.

Why doesn’t up 50% then down 50% return to the start?

Because the base differs each time: 100 up 50% is 150, then down 50% discounts 150 to 75 — a classic percentage intuition trap.