How do I work out a 20% discount on a $250 product?

Choose "Apply a discount of X%", enter 20 and 250. The result is 200: the final price is $200 and you save $50.

How do I find the original price after a discount?

Use "Value before a discount": enter the discount percentage and the value you paid. If you paid 80 with 20% off, the original price was 100.

Can the change be negative?

Yes. When the final value is lower than the starting one, the change is negative and shows a drop, like −20% from 100 to 80.

Why does a message say the calculation is not possible?

Some calculations do not exist with certain numbers, such as dividing by zero (for example, "5 is what % of 0" or a change starting from zero). Check the values you entered.

Percentage calculator: discount, increase and change

Updated on October 30, 2026

Pick the calculation you need (what is X% of a value, discount, increase, percentage change or the original value), enter the two numbers and see the result with the formula used. It works on your phone and your numbers never leave your browser.

What to calculate

Percentage (%)

Total value

Fill in both fields to see the result.

The text is processed in your browser and is not sent anywhere.

How to use it

Under "What to calculate", choose the calculation. The field names change to match it.
Enter the two numbers. Use a point or a comma for decimals.
Read the result and the sentence explaining the calculation, with the formula used right below.
Copy the sentence or save it to a note, for example to keep the math of a purchase.

The seven calculations, with examples

What is X% of a value: 15% of 200 is 30. Formula: total × percentage ÷ 100.
One value is what % of another: 30 is 15% of 200. Formula: part ÷ total × 100.
Percentage change: from 80 to 100, the change is +25%. From 100 to 80, it is −20%. Formula: (final − starting) ÷ starting × 100.
Increase by X%: 250 increased by 10% becomes 275. Formula: value × (1 + percentage ÷ 100).
Discount of X%: 250 with 20% off comes to 200, and you save 50. Formula: value × (1 − percentage ÷ 100).
Value before an increase: if the current price is 125 after a 25% increase, the old value was 100. Formula: current value ÷ (1 + percentage ÷ 100).
Value before a discount: if you paid 80 with 20% off, the original price was 100. Formula: current value ÷ (1 − percentage ÷ 100).

Shortcuts for mental math

10%: divide the value by 10. 10% of 340 is 34.
1%: divide by 100. 1% of 340 is 3.40.
50%: it is half. 25% is half of half.
5%: it is half of 10%. 15% is 10% plus 5%.
A 10% tip: move the decimal point one place to the left.

Watch out for percentages

A 10% increase followed by a 10% discount does not bring you back to the original value: 100 becomes 110 and, with 10% off, 99. The discount applies to a bigger value. So to undo an increase, applying the same percentage backwards is not enough: use "Value before an increase".

Also do not confuse percentage change with percentage points. If a rate goes from 10% to 12%, it rose 2 percentage points, but the percentage change is +20% (2 ÷ 10). News and ads often mix the two up, and the difference changes the conclusion.

Frequently asked questions

How do I work out a 20% discount on a $250 product?: Choose "Apply a discount of X%", enter 20 and 250. The result is 200: the final price is $200 and you save $50.
How do I find the original price after a discount?: Use "Value before a discount": enter the discount percentage and the value you paid. If you paid 80 with 20% off, the original price was 100.
Can the change be negative?: Yes. When the final value is lower than the starting one, the change is negative and shows a drop, like −20% from 100 to 80.
Why does a message say the calculation is not possible?: Some calculations do not exist with certain numbers, such as dividing by zero (for example, "5 is what % of 0" or a change starting from zero). Check the values you entered.