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Percentage calculator

Exact decimal math

Five everyday percentage questions in one place: A% of B, A as a percent of B, the percent change from A to B, and B plus or minus A% (markups and discounts).

Try:

Fill in the fields to see the result.

How to use it

  1. Choose the question you want answered.
  2. Enter A and B; the answer updates as you type.
  3. Copy the result, or use a sample to see each kind.

Details

A% of B
B × A ÷ 100
A is what % of B
A ÷ B × 100
% change
(B − A) ÷ |A| × 100
Discount
B × (1 − A ÷ 100)

Questions

How do I calculate a percentage increase?

Subtract the old value from the new one, divide by the old value and multiply by 100. From 80 to 100 is (100 − 80) ÷ 80 × 100 = 25%.

Why is a 50% rise followed by a 50% fall not back to the start?

The fall is taken from the bigger number. 100 + 50% = 150, and 150 − 50% = 75. Percent changes multiply rather than add.

How do I work out 20% off a price?

Choose 'B minus A%', put 20 in A and the price in B. $59.99 less 20% is $47.99 (rounded to cents).

What's the difference between percent and percentage points?

Going from 4% to 5% is a rise of 1 percentage point but 25 percent. The calculator gives percent; subtract the two rates for points.

Is what I type sent anywhere?

No. The calculation runs in this browser tab with the same code our MCP server uses. Nothing you type is sent to a server or saved, apart from settings like filing status, which stay in this browser.

Can an AI agent use this?

Yes. The same function is a tool on our free MCP server at tools.cuelark.com/mcp, so ChatGPT, Claude or Cursor get exactly the answer this page shows. 'Copy MCP call' gives you the arguments.