Increase or Decrease a Number by a Percentage
Use this calculator when you know the starting number and the percent to apply. It returns the new total and the amount that was added or subtracted. Sales tax and simple markups are this operation with different labels.
How this is calculated
Multiply the number by one plus the rate to increase, or by one minus the rate to decrease.
new value = number × (1 ± percent / 100)
- Convert the percent to a decimal. 15% is 0.15.
- For an increase, multiply by 1.15. 200 × 1.15 = 230, so the amount changed is 30.
- For a decrease, multiply by 0.90. 80 × 0.90 = 72, so the amount changed is −8.
15% of 200 is 30, which is the amount changed on an increase. This tool adds that portion back onto the original. To recover the original from 230 after a 15% increase, use reverse percentage.
Not the same as
Applying a percent and measuring a change are inverse jobs.
- What is X percent of Y? That tool returns only the percent portion. This tool returns the original plus or minus that portion. Open percent of a number
- Reverse percentage Reverse percentage starts from the final amount. This tool starts from the original. Open reverse percentage
Related tools
Apply-a-percent questions
230. The amount changed is 30.
72. The amount changed is 8.
No. 100 becomes 110, then 99. Use reverse percentage if you need the true original.
Percent of 200 at 15% is 30. This tool returns 230, the total after adding that 30.
Yes for a simple add-on tax. The sales tax calculator uses the same multiply-by-1-plus-rate math with tax labels.
Use percentage change, not this tool.