Calculate percentage increase or decrease between two values with step-by-step formula breakdown and reverse calculation.
You enter an original value and a new value; the tool subtracts them, divides by the original value, multiplies by 100, and reports the result as a signed percentage along with the raw difference. A reverse mode lets you enter one value plus a known percentage change to solve for the other. The most common surprise: percentage change is not symmetric. Dropping from 100 to 50 is a 50% decrease, but climbing back from 50 to 100 is a 100% increase, not 50%, because the base value changes between the two calculations.
A concrete input and expected output from the current implementation.
Input
Old value: 80, New value: 100
Expected output
+25.00% change (an increase of 20)
(100 - 80) / 80 = 0.25, and 0.25 x 100 gives a 25% increase relative to the original value of 80.
The core calculation is (new - old) / old x 100. A positive result is reported as an increase, a negative result as a decrease. The step-by-step breakdown shows the difference (new minus old) and the division step separately, so you can see where the sign and magnitude come from rather than just the final percentage.
Given an original value and a target percentage change, the tool solves new = old x (1 + p/100) to find the resulting value. Given a new value and a percentage change, it rearranges to solve for the original value. This is the direction people need when they know a discount rate or growth rate and want the actual dollar figure.
Because each percentage is calculated against a different base. A 50% increase on 100 gives 150; a 50% decrease on 150 (not 100) gives 75. The two percentages share a label but not a denominator, so they don't cancel out.
No, not directly. This tool computes relative percentage change, not the simple subtraction used for percentage points. If you have two rates like 5% and 8%, the percentage point difference is just 3, but this tool will instead report the relative change between 5 and 8, which is 60%.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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