How to add a percentage to a number

Formula

To increase a value by p percent:

new value = original value x (1 + p / 100)

Adding 18% to 500 gives:

500 x 1.18 = 590

The increase is 90 and the new value is 590. The multiplier shortcut prevents an extra subtraction or addition step: add 12% by multiplying by 1.12, 25% by 1.25, and 100% by 2.

Avoid these mistakes

• Adding the number 18 when the instruction means 18% of the original value.
• Using the final value as the percentage base.
• Applying several increases by simply adding their percentages. Successive changes use successive multipliers.
• Assuming that equal increases and decreases cancel each other.

For the change between an old and new value, use percentage increase. To calculate an amount directly, use the percentage calculator.