Find the percent change between any two numbers
💡 Why This Matters This is different from a basic percentage calculator — instead of finding "X% of Y," this finds how much something changed, in percent terms, between two values. Useful for tracking price changes, growth rates, salary raises, or any before-and-after comparison.
Percentage changes aren't symmetric — a 50% increase followed by a 50% decrease doesn't bring you back to where you started, because each percentage is calculated on a different base number. Going up 50% then down 50% actually leaves you 25% below your original value.
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Percentage change is calculated with the formula ((New Value − Old Value) ÷ Old Value) × 100. Subtracting the old value from the new value tells you the raw difference; dividing by the old value expresses that difference relative to where you started; multiplying by 100 converts it into a percentage. If the new value is larger, the result is positive (an increase); if smaller, it's negative (a decrease).
The large number is your percent change — positive for an increase, negative for a decrease. The breakdown underneath shows both the old and new values you entered, so you can double-check the comparison at a glance. A 25% result means the new value is 25% higher than the old one; a -25% result means it's 25% lower.
Percentage change is always relative to the old value, not a fixed amount — this is why sequential percentage changes (like a 20% increase followed by a 20% decrease) don't cancel out to zero. Also, percentage change becomes misleading or undefined when the old value is zero or negative, since you can't meaningfully express a percent change from nothing or from a negative starting point using this formula.
Use this to track price changes, compare growth between two time periods, evaluate salary increases, or measure any before-and-after difference. When comparing multiple changes over time, remember each one is relative to its own starting point — stack them carefully rather than simply adding percentages together.
Example (increase): Say a price goes from $80 to $100. Change = (($100 − $80) ÷ $80) × 100 = +25%, a 25% increase.
Example (decrease): Say a price goes from $100 to $80. Change = (($80 − $100) ÷ $100) × 100 = −20%, a 20% decrease. Notice this isn't the same 25% — the direction you're comparing matters.
A regular percentage calculator answers questions like "what is 20% of 50?" This calculator answers a different question: "by what percent did a value change?" — comparing an old number to a new number to find the percent increase or decrease between them.
Subtract the old value from the new value, divide that by the old value, then multiply by 100. If the result is positive, it's a percent increase; if negative, it's a percent decrease. Formula: ((New − Old) / Old) × 100.
Because each percentage is calculated on a different base value. A 50% increase on 100 gives 150. A 50% decrease is then calculated on 150, not the original 100, giving 75 — not back to 100. Percentage changes are relative to whatever the current value is at that moment.