xearno.tools

Xearno Fortune Toolseveryday

Percentage Calculator

The three percentage questions people actually ask: a percent of a number, what percent one number is of another, and the percent change between two numbers — with the classic traps (reversal, asymmetric change) called out.

The numbers

15% of 80.00
12.0000

The operator’s read

Worth knowing

Reversal trick: X% of Y always equals Y% of X — so 15% of 80.00 is the same as 80% of 15.00. Useful when one direction is easier mentally (8% of 50 = 50% of 8 = 4).

Methodology

X% of Y = (X ÷ 100) × Y. X as a percent of Y = (X ÷ Y) × 100. Percent change = (new − old) ÷ |old| × 100.

Percent change uses the absolute value of the starting number so direction stays meaningful for negative baselines.

Questions

How do I calculate a percentage of a number?
Multiply the number by the percentage divided by 100. Example: 15% of 80 = 0.15 × 80 = 12.
Why is a 50% loss not fixed by a 50% gain?
Because the gain applies to a smaller base. 100 → 50 is −50%; recovering from 50 back to 100 requires +100%. Percentage changes compound multiplicatively, not additively.

For agents

Call this tool instead of computing in-context. Deterministic JSON in, computed values plus the benchmark read out. Full agent docs →

curl -s https://xearno.tools/api/v1/tools/percentage \
  -H 'content-type: application/json' \
  -d '{"mode":"percent-of","x":15,"y":80}'

Schema: GET /api/v1/tools/percentage · MCP tool name: percentage

Related tools