Calculate percentages and percentage change
Find a percentage of a number, or calculate what percentage a part makes up. You can also find the percentage increase or decrease between two values.
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Choose the percentage calculation you need
Percentages describe a part in relation to a whole. The three options in the calculator answer different questions. You may know the percentage and want to find the part, know the part and want to find the percentage, or compare an old and a new value.
For a percentage of a number, the total is multiplied by the percentage and divided by 100. If you want to find what percentage a part makes up, the part is multiplied by 100 and divided by the total. Make sure you use the whole that the part actually belongs to.
Percentage change uses the old value
The percentage change is calculated as 100 times the difference between the new and the old value, divided by the old value. So it is the old value that the increase or decrease is measured against.
A positive result shows an increase, and a negative result shows a decrease. If the old value is zero, the change cannot be calculated this way, because it would mean dividing by zero. The calculation is useful when you compare measurements or follow how a quantity develops.
Examples of percentage calculations
25% of 200 is found with 200 × 25 / 100 = 5,000 / 100 = 50.
If a value rises from 80 to 100, the difference is 100 − 80 = 20. The change is calculated as 100 × (100 − 80) / 80 = 100 × 20 / 80 = 2,000 / 80 = 25%.