Percentage Calculator
Simple percentage calculator: find X% of Y, what percentage A is of B, and percentage increase or decrease.
What is X% of Y?
A is what % of B?
% increase / decrease
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What to work out next
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Three of the most common percentage questions, in one place: what is X% of Y, what percentage is A of B, and the percentage change from one number to another.
What this calculator does
Handles the three percentage questions that come up constantly in a business: what is X% of a number, what percentage one number is of another, and the percentage increase or decrease between two numbers.
Who it is for
- Operators checking service charge, deposit percentages or a supplier's price rise.
- Managers comparing this week's sales with last week's in percentage terms.
- Anyone sanity-checking a discount or uplift before agreeing to it.
How to use it
- Pick the mode that matches your question.
- Enter the two figures - the calculator handles the ordering for you.
- For change calculations, put the original ('from') value first and the new ('to') value second.
The formula
- X% of Y = Y x (X / 100)
- A as a percentage of B = (A / B) x 100
- Percentage change = ((New - Old) / Old) x 100
Worked example
A 12.5% service charge on an £86.00 food and drink bill, and a sales comparison between last month's £4,200 and this month's £4,830.
- Service charge = £86.00 x 0.125 = £10.75, so the total is £96.75
- Sales change = (£4,830 - £4,200) / £4,200 = 0.15
- 0.15 x 100 = 15%
The service charge is £10.75 and month-on-month sales are up 15%.
How to read your result
- Percentage change is always measured against the earlier figure, so a rise and the equivalent fall are not the same percentage.
- A 20% drop followed by a 20% rise does not return you to the starting figure - it leaves you 4% down.
- Percentage point differences (GP moving from 68% to 70%) are not the same as a percentage change (that is a 2.9% increase in the GP figure).
What to do next
- When a supplier announces a price increase, convert it to pounds per week on your actual usage before accepting it.
- Track weekly sales change as a percentage, not just in pounds, so seasonality is easier to read.
- Use the 'A as a % of B' mode to turn any cost line into a percentage of net sales for your P&L.
Common mistakes to avoid
- Calculating change against the new figure instead of the original.
- Adding percentages that have different bases, such as a 10% discount and a 12.5% service charge.
- Confusing percentage points with percentages when discussing margin movements.
Assumptions and limitations
- Results are rounded to two decimal places for display.
- Percentage change from a starting value of zero is undefined.
Dumb Bambi provides general business information, not accounting, tax or legal advice. Read our calculation methodology or tell us about a mistake.
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Frequently asked questions
How do I calculate a percentage increase?+
Subtract the old number from the new, divide by the old, then multiply by 100.
Is a negative percentage a decrease?+
Yes - a negative percentage means the value has gone down.