Why direction matters
Going from 80 to 100 rises by 25%. Going from 100 back to 80 falls by 20%. The difference is still 20, but the starting value changes.
PERCENTAGE TOOL
Free online percentage calculator.
Find percentage change or apply a percentage. No download or account needed.
02
The difference
%
A little change, explained.
Enter your original and new values
to see how much changed.
THE MATH, MADE SIMPLE
Change needs a starting point.
Enter an original value and a new value to find the percentage increase or decrease and the absolute change. The same difference can mean something very different depending on where you begin.
FOR A POSITIVE STARTING VALUE
New − OriginalOriginal
× 100WORKED EXAMPLE · 80 TO 100
A change of 20. An increase of 25%.
Subtract the original value from the new value: 100 − 80 = 20. Divide that change by the original 80, then multiply by 100.
(100 − 80) ÷ 80 × 100 = 25%
These are example numbers. Your own calculation and formula appear in the calculator’s result above.
Percent vs. percentage points
A rate going from 10% to 15% rises by 5 percentage points. Relative to the original 10%, that’s a 50% increase.
Zero and negative values
A zero original has no defined percentage change, even from 0 to 0. For a negative original, divide by its magnitude: −100 to −50 is a 50% upward movement. This is a magnitude-based convention, not a standard growth rate. Interpret crossing zero carefully.
Understanding the absolute change
Absolute change here means the signed difference, new minus original. A positive result moves upward; a negative result moves downward. Equal values have zero difference and, for a nonzero original, 0% change. Compare numbers in matching units. Results are approximate and rounded; very small or large values use scientific notation.
THE MATH, MADE SIMPLE
One percentage. Two useful numbers.
Enter a starting value and a percentage, then choose Increase or Decrease. Multiply the starting magnitude by the percentage, then add or subtract that amount to get the new value.
CHANGE AMOUNT
|Starting value| × Percentage100
WORKED EXAMPLE · 80 WITH A 25% INCREASE
A change amount of 20. A new value of 100.
25% of 80 is 20. Add that amount to the starting value for Increase, or subtract it for Decrease.
80 × 25 ÷ 100 = 20
Increase80 + 20 = 100
Decrease80 − 20 = 60
These are example numbers. Your own change amount, new value, and formula appear in the calculator’s result above.
Why reversing a change differs
A 25% increase takes 80 to 100. A 25% decrease from 100 gives 75, not 80, because the percentage now uses a different starting value. A 20% decrease from 100 returns to 80.
Percent vs. percentage points
Applying a 50% increase to a rate of 10% gives 15%. That is a rise of 5 percentage points. Enter 10 as the starting value and 50 as the percentage; entering 5 would apply a 5% relative increase instead.
Zero and negative starting values
Any percentage of zero is zero, so a zero start stays zero. For a negative start, use its magnitude: 50% of |−100| is 50. Increase adds 50 to give −50; Decrease subtracts 50 to give −150. Increase always moves upward and Decrease downward, unless the amount is zero.
Work out a tip and the total
For a bill of 60 and a 20% tip, choose Apply a %, enter 60 as the starting value and 20 as the percentage, then choose Increase. The change amount is the tip: 60 × 20 ÷ 100 = 12. The new value is the bill plus tip: 60 + 12 = 72. Use the bill amount you want to base the tip on, and check whether a service charge is already included. You choose the tip percentage; the calculator simply does the math.
Zero, negative, and large percentages
A 0% adjustment leaves the starting value unchanged. Enter a percentage of zero or more and use the direction selector rather than a negative percentage. Percentages above 100 are allowed: a 150% decrease from 80 subtracts 120, giving −40. The change amount is a magnitude, with its Added or Subtracted label showing the direction. Values are unit-neutral; results are approximate and rounded.
About Percentage Tool
Percentage Tool is operated by Chris Holcomb.
Find the percentage change between two values, or apply a percentage to a starting value and see both the change amount and new value. Use this free online percentage calculator with numbers in any matching units. It runs in your browser with no download, installation, or account needed. Absolute change here means the signed difference, new minus original; its size is the distance between the values.
Results are approximate and rounded for readability. Very small or large results use scientific notation. Compare values in matching units and use the context to interpret the result.
Privacy
Last updated September 6, 2026.
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