Calculate the percentage increase or decrease between any two values instantly.
Percentage change measures how much a value has increased or decreased relative to its original value, expressed as a percentage. It answers the question: "by what percent did this number change?" A positive result indicates an increase; a negative result indicates a decrease.
The formula divides the absolute difference (new minus original) by the absolute value of the original, then multiplies by 100. Using the absolute value in the denominator is essential — without it, a negative original value would flip the sign of the result, making an increase appear as a decrease.
Percentage change is one of the most universally searched calculations on the internet because it appears constantly in everyday contexts: stock price movements, salary changes, inflation comparisons, test score improvements, population statistics, and business performance reporting. Any time a number changes over time, percentage change quantifies that movement in a standardized, comparable way.
These two calculations are frequently confused. Percentage change has a direction — it tells you how a value moved from a specific starting point. Percentage difference is symmetric — it measures how far apart two values are relative to their average, with no implied direction or "before/after" relationship.
Use percentage change when one value is clearly the original and the other is the new or updated value: last year's revenue vs this year's, your weight six months ago vs today, yesterday's stock price vs today's. Use percentage difference when comparing two independent values with no inherent order: the price at two different stores, the test scores of two different students.
Stock market: a stock that fell from $80 to $60 experienced a -25% change (not -20%). The difference is $20, and $20/$80 = 0.25 = 25% decline. This calculation correctly captures the magnitude of loss relative to what you started with.
Salary negotiation: if your salary increases from $65,000 to $72,000, the percentage change is ($72,000-$65,000)/$65,000 × 100 = 10.77%. Knowing this number precisely helps you evaluate offers and negotiate confidently.
Inflation: when the Consumer Price Index rises from 280 to 298, inflation for that period was (298-280)/280 × 100 = 6.4%. This is exactly how official inflation figures are calculated by statistical agencies worldwide.
The most common error is reversing the numerator and denominator — dividing the original by the difference instead of the difference by the original. Another frequent mistake is using the new value in the denominator instead of the original. Always remember: you're measuring change relative to where you started, so the original value goes in the denominator.
A subtler error occurs with negative original values. If a company's net income was -$10 million last year and is -$6 million this year (an improvement), the percentage change is (-6-(-10))/|-10| × 100 = 4/10 × 100 = 40% improvement. The absolute value in the denominator preserves the correct sign.