CalcQuick · Percentage
Percentage Calculator
Choose percent of an amount, percentage change, symmetric percentage difference, increase or discount, or reverse percentage. Every result updates as you type.
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How to use this calculator
- Enter your values using the units shown.
- Review the result, which updates instantly.
- Check the formula and assumptions before using the number for a decision.
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Formula and assumptions
Percent of an amount = (p ÷ 100) × amount. Percentage change = ((new − old) ÷ |old|) × 100. Percentage difference = |a − b| ÷ ((|a| + |b|) ÷ 2) × 100. Adjusted value = start × (1 ± p ÷ 100).
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Worked example
15% of 240 is 36. A 15% discount on 200 gives 170. If 170 is the value after a 15% discount, the original value is 170 ÷ 0.85 = 200.
FAQ
Frequently asked questions
How do I add a percentage to a number?
Multiply the number by 1 plus the percentage as a decimal. To add 15% to 200, calculate 200 × 1.15 = 230.
Why can’t percentage change start at zero?
The formula divides by the original value. When it is zero, percentage change is undefined even though the absolute change can still be shown.
How do I find the original value before a discount?
Divide the final value by 1 minus the discount rate as a decimal. If 170 is the price after a 15% discount, the original value is 170 ÷ 0.85 = 200.
Why can’t I add the discount percentage back to the final value?
The discount was calculated from the original value, while adding the same percentage uses the lower final value as its base. Reverse the discount by dividing by 1 minus the discount rate instead.
What is the difference between percentage difference and percentage change?
Percentage difference treats two values symmetrically and divides their absolute gap by their average magnitude. Percentage change uses the old value as the reference and can be positive or negative.