Is ToolFlow really free?

Yes. Every tool is completely free with no limits, sign-up or installation.

Many tools process files directly in your browser so data never leaves your device.

How do I work out a percentage of a number?

Multiply the number by the percentage and divide by 100. For 15 percent of 240, that is 240 times 15 divided by 100, which is 36.

How do I calculate percentage change?

Subtract the old value from the new one, divide by the old value, and multiply by 100. A price that goes from 80 to 100 has changed by 20 divided by 80, which is 25 percent.

What is the difference between percentage change and percentage difference?

Percentage change has a direction: it measures how far a value moved from an original. Percentage difference is symmetric. It compares two values when neither is the original, by dividing their gap by their average.

Why is a 50 percent increase followed by a 50 percent decrease not back to the start?

Because the second percentage is taken from a bigger number. 100 up by 50 percent is 150. Down by 50 percent from 150 is 75, not 100.

How do I add VAT or tax to a price?

Work out the tax as a percentage of the price and add it. For 20 percent VAT on 99, the tax is 19.80, so the total is 118.80.

Does the calculator work on my phone?

Yes. It runs in your browser and updates as you type.

How to Calculate Percentage Increase and Decrease

Percentages show up everywhere: a sale sign, a restaurant bill, a pay rise, an exam result. The sums are not hard, but it is easy to use the wrong one. Most of the confusion comes from not knowing which question you are really asking. This guide covers the five calculations people need most, with the formula in words and a worked example for each.

1. What is X percent of Y?

Multiply Y by X and divide by 100.

Example: What is 15 percent of 240? 240 times 15 divided by 100 is 36.

This is the sum behind discounts and tax. A 20 percent discount on a 150 item is 150 times 20 divided by 100, which is 30, so you pay 120.

2. X is what percent of Y?

Divide X by Y and multiply by 100.

Example: 30 is what percent of 200? 30 divided by 200 is 0.15, and times 100 is 15 percent.

Use it for grades. If you scored 67 out of 80, that is 67 divided by 80 times 100, which is 83.75 percent.

3. Percentage change (increase or decrease)

Subtract the old value from the new one, divide by the old value, and multiply by 100. A positive answer is an increase and a negative one is a decrease.

Example: A price goes from 80 to 100. The change is 20, and 20 divided by 80 is 0.25, so it is a 25 percent increase. A price that goes from 45 to 54 rises by 9, and 9 divided by 45 is 20 percent.

Always divide by the old value, not the new one. That is the most common slip.

4. Percentage difference

When neither number is the starting point, such as comparing two products or two schools, use percentage difference. Divide the gap between the two numbers by their average, then multiply by 100.

Example: 40 and 50. The gap is 10. The average is 45. 10 divided by 45 is 22.22 percent.

The answer is the same whichever number you put first, which is exactly why it is used for comparisons without a direction.

5. Increase or decrease a number by a percentage

To increase, multiply by one plus the percentage as a decimal. To decrease, multiply by one minus it.

Example: 250 increased by 20 percent is 250 times 1.20, which is 300. Decreased by 20 percent it is 250 times 0.80, which is 200.

A salary of 32,000 with a 5 percent rise becomes 32,000 times 1.05, which is 33,600.

How to do all five with ToolFlow

Open the Percentage Calculator.
Choose the calculation that matches your question: percent of a number, what percent, percentage change, percentage difference, or increase and decrease.
Type your numbers. The answer updates as you type.

Real situations

A sale: 20 percent off 150. Discount 30, final price 120.
VAT: 20 percent on 99. Tax 19.80, total 118.80.
A grade: 67 out of 80 is 83.75 percent.
A price rise: 45 to 54 is a 20 percent increase.
A pay rise: 32,000 plus 5 percent is 33,600.

Mistakes that catch people out

Dividing by the wrong number. Percentage change always divides by the starting value.
Thinking up and down cancel out. A 50 percent rise followed by a 50 percent fall leaves you at 75 if you started at 100, because the second change is taken from 150.
Mixing up percent and percentage points. If a rate goes from 4 percent to 6 percent, it rose by 2 percentage points, which is a 50 percent increase.
Using change when you meant difference. If there is no clear original, use percentage difference.
Taking tax off the wrong way. To remove 20 percent VAT from a price that already includes it, divide by 1.20. Taking 20 percent off the total gives the wrong answer.

Check your answer

A quick sense check helps. 10 percent of a number is that number with the decimal point moved one place left, so 10 percent of 240 is 24. If your answer for 15 percent came out lower than 24 or far above 36, something is off. A calculator catches slips like these in seconds.