How to Calculate Percentages, Discounts, and Change
Calculate a percentage of a number, percentage relationships and percentage increase or decrease.
What to know before you start
Percentage change from an original value of zero is undefined. Rounding can make displayed results differ slightly from spreadsheet or financial-system rules.
Recommended workflow
- Choose the percentage question first: percent of a value, one value as a percent of another, or increase/decrease.
- Use the original value as the denominator for conventional percentage change; when it is zero, report the raw change instead of inventing a percent.
- Keep enough decimal places for the task, then round only at the final presentation step.
How to check the result
Recheck the result against the original input and the rule you intended to apply. Percentage change from an original value of zero is undefined. Rounding can make displayed results differ slightly from spreadsheet or financial-system rules.
Common mistakes
Common failures come from wrong units, ambiguous assumptions, changing the rule after seeing a result, or using a quick browser workflow where a regulated or specialist process is required.
Frequently asked questions
How do I calculate 20% of 150?
Multiply 150 by 0.20; the result is 30. The calculator can do this directly.
What is the percentage change formula?
For a non-zero starting value: (new − old) ÷ old × 100.
Percentage Calculator
Calculate a percentage of a number, percentage relationships and percentage increase or decrease.
Open the related toolPercentage Calculator
Calculate a percentage of a number, percentage relationships and percentage increase or decrease.
Open Percentage Calculator