％Percentage Calculator
Calculate X% of Y, what percent X is of Y, and the percent change between two values — with step-by-step working shown.
Worked examples
15% of 200
GET /api/v1/calculators/percentage-calculator?x=15&y=200&op=percent_of
Result: 30
45 is what percent of 360
GET /api/v1/calculators/percentage-calculator?x=45&y=360&op=what_percent
Result: 12.5%
Percent change from 80 to 96
GET /api/v1/calculators/percentage-calculator?x=80&y=96&op=change
Result: 20% increase
Machine API (x402)
$0.001 / callThis tool is also a JSON API for AI agents. Requests without payment receive 402 Payment Required plus instructions; agents pay USDC on Base via the x402 protocol — no accounts, no API keys.
GET /api/v1/calculators/percentage-calculator?x=15&y=200&op=percent_of HTTP/1.1
Host: agenttools-hub.vercel.app
→ 402 (payment required, instructions in headers)
→ 200 (after X-PAYMENT header; JSON body below)
{
"tool": "calculators/percentage-calculator",
"input": {"x":15,"y":200,"op":"percent_of"},
"result": { "value": 30, "answer": "30" }
}Agent docs: /llms.txt · OpenAPI spec · integration guide
About this tool
Three percentage calculations in one tool: find X% of a number, express one number as a percentage of another, or measure the percent change between two numbers. Every result includes the derivation steps.
X% of Y = X ÷ 100 × Y · X as % of Y = X ÷ Y × 100 · % change = (Y − X) ÷ |X| × 100
Frequently asked questions
How do I calculate X% of Y?
Divide X by 100, then multiply by Y. For example 15% of 200 = 15 ÷ 100 × 200 = 30.
How is percent change calculated?
Subtract the old value from the new value, divide by the absolute old value, and multiply by 100. A negative result is a decrease.
Why is percent change from 0 undefined?
The formula divides by the starting value. Starting from zero, any change is infinitely large in percentage terms, so the operation is undefined.