Business
Percentage Calculator
Three percentage sums in one place, each one showing the arithmetic and not just the answer.
15% of 240 = 15 ÷ 100 × 240 = 36
300 − 240 = 60; 60 ÷ 240 × 100 = 25% increase
Percentages arrive in three shapes and most people end up reaching for a different tool for each one: a discount off a price, one number as a share of another, and the change between two values. All three are the same arithmetic rearranged, which is why they belong on a single page.
Every field recalculates on the keystroke, and the line under the answer shows the sum that produced it — the percentage over a hundred multiplied by the base, the division and multiplication for a share, the difference over the starting value for a change. That last part matters more than it sounds: an answer you cannot check is an answer you end up redoing on a phone calculator.
How to use it
- Pick the sum you want with the tabs: X% of Y, X is what % of Y, or Increase or decrease.
- Type into the fields. The answer and the working under it update as you go — there is no button to press.
- For a change, put the starting value in the first field and the new value in the second. A rise is shown with a plus sign; a fall is labelled as a decrease.
- The working line is plain text, so you can copy it into a document if somebody wants to see how the figure was reached.
Questions
How is a percentage change calculated?
New value minus old value, divided by old value, times a hundred. Going from 240 to 300 is 60 ÷ 240 × 100 = 25%. Going the other way, from 300 to 240, is −60 ÷ 300 × 100 = −20%: the same 60, a different percentage, because the base changed. This tool always divides by the starting value, which is the convention that makes a rise and a fall of the same size report different numbers.
Why can't I work out a change from zero?
Because a percentage change is a fraction of the starting value. With a starting value of zero there is nothing to divide by — going from 0 to 50 is an infinite increase, not a very large finite one. The tool says so rather than printing a number that means nothing.
What is the difference between percent and percentage points?
A move from 4% to 5% is one percentage point and also a 25% increase. Both are correct and they describe different things: subtract for the points, use the increase or decrease tab for the relative change.
Does it handle decimals and negative numbers?
Yes. Anything you can type into a numeric field is accepted, and answers are rounded to six decimal places for display only — the calculation itself is done in full, so a figure you copy out is not carrying rounding error from an earlier step.