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EVERYDAY TOOLS

Percentage calculator

Work out a discount, percentage or percentage change.

● Processed in your browser

What is this tool?

Work out a percentage amount, a discounted price or a percentage change. The same two numbers can answer different questions, so selecting the operation is as important as entering the values correctly.

How to use it

  1. Read the input labels and limits below, then choose the operation that matches your task.
  2. Choose the percentage operation that matches your question.
  3. Read the current field labels and enter the relevant original value and percentage or new value.
  4. Calculate and review whether the output is an amount, final price or percentage.
  5. Check the result against the worked example or original file before copying, downloading or using it elsewhere.

Worked example

A change from 80 to 100 is a 25% increase because the difference is compared with 80. Returning from 100 to 80 is a 20% decrease. Percentage changes depend on which value is the starting point.

Questions & limits

How it works

Choose an operation and enter two values. Percentage of a number uses value × percentage ÷ 100. Discount subtracts that amount from the original price. Percentage change uses (new − old) ÷ old × 100.

A practical example

A 20% discount on 1,500 saves 300 and gives a final price of 1,200.

Know the limits

Percentage change is undefined when the old value is zero. Values are rounded for display, and this calculator does not apply taxes or currency conversion.

Documentation updated October 4, 2026.

How is a discount calculated?

A discount of 20% on 100 removes 20 and leaves 80. Choose the matching operation and enter the percentage and original amount in their labelled fields.

Why is percentage change from zero undefined?

The usual formula divides the difference by the original value. When that original value is zero, there is no finite percentage change under that formula.

Checking your result

Read the labels before entering a value, especially when switching an operation or unit. Start with a simple example whose answer you already know if you are unsure which mode to use. After changing an input, check that you are reading the new result rather than a value copied earlier. Invalid or incomplete inputs need correcting before the calculation can finish. For a form or deadline with specific rules, follow the destination’s requirements and use this page as a convenient calculation aid.

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Features & limits

Choose percentage of a number, percentage change or discount. Percentage change needs a non-zero original value. Discounts must be from 0–100%. A change from a negative starting value needs careful interpretation; always keep the original figures alongside the answer.

This tool runs in a modern browser with JavaScript enabled. It processes the values or files you enter on your device. Loading the site still makes hosting requests. The separate contact form sends messages to the administrator; it is not part of tool processing. Keep an original copy and inspect any exported result before relying on it.

Frequently asked questions

Why is percentage change from zero undefined?

The usual formula divides the difference by the original value. When that original value is zero, there is no finite percentage change under that formula.

What can I use percentage calculator for?

Work out a percentage amount, a discounted price or a percentage change. The same two numbers can answer different questions, so selecting the operation is as important as entering the values correctly.

What are this tool’s limits?

Choose percentage of a number, percentage change or discount. Percentage change needs a non-zero original value. Discounts must be from 0–100%. A change from a negative starting value needs careful interpretation; always keep the original figures alongside the answer.

Can I try a worked example?

A change from 80 to 100 is a 25% increase because the difference is compared with 80. Returning from 100 to 80 is a 20% decrease. Percentage changes depend on which value is the starting point.

Do I need an account or upload my input?

No tool account is required. Processing takes place in your browser; your tool input is not sent to the contact inbox. Use a trusted device, keep your originals and avoid including passwords or private credentials in examples.

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