Percentage Change Calculator

Percentage change calculator for increases and decreases

If you are comparing two numbers and want to know how much something changed in percentage terms, this calculator is the standard way to do it. Typical uses include price changes, salary adjustments, sales growth, inflation comparisons, weight changes, interest rate shifts, and any before and after situation where you want a single percent figure that is easy to communicate.

You enter an original value (the starting point) and a new value (the ending point). The calculator returns the percentage change, tells you whether it is an increase or decrease, and also shows the absolute difference in the same units as your inputs. That second number matters because a 10% change can mean very different things depending on the base. A 10% change on 10 is 1. A 10% change on 10,000 is 1,000.

This calculator also shows the ratio between the new and original values. That ratio is useful when you need a quick “times bigger” sense check. For example, if the ratio is 1.25, the new value is 1.25× the original. If the ratio is 0.80, the new value is 80% of the original.

Assumptions and how to use this calculator

• The standard formula used is: (new − original) ÷ original × 100.
• If the original value is 0, percentage change is undefined, so the calculator will ask you to use a non-zero baseline.
• Negative values are allowed, but interpretation changes (for example, moving from −100 to −50 is an “increase” numerically but may represent a smaller loss). Use the absolute change alongside the percentage.
• Results are rounded to two decimals to keep them readable. Small inputs can look jumpy due to rounding.
• This tool assumes both numbers are in the same unit (for example both are prices, both are kilograms, or both are counts). It does not convert units.

Common questions

What is the difference between percentage change and percentage difference?

Percentage change treats one number as the baseline (the original) and measures how far the new value moved relative to that baseline. Percentage difference is often used when neither value is clearly the “starting point,” and it typically divides by the average of the two values instead of the original. If you have a clear “before and after,” percentage change is usually the right choice.

Why does the calculator reject an original value of zero?

Percentage change divides by the original value. Dividing by zero is not defined, so there is no meaningful percent result. If your baseline is genuinely zero, you can still look at the absolute change (new minus original), or choose a different baseline that represents a real starting point.

How should I interpret percentage change when numbers are negative?

The math still works, but the meaning can be confusing. If your original is negative, the sign of the denominator affects the sign of the percentage. In practical terms, rely on three things together: the direction label (increase or decrease), the absolute change, and your real-world context (profit versus loss, debt versus credit, temperature below zero, and so on).

Is a 50% decrease the same as a 50% increase back to the original?

No. If something drops 50% from 100 to 50, it needs a 100% increase to return from 50 to 100. Percent changes are not symmetric because they use the starting value as the base each time.

How can I make the result more useful for decisions?

Always look at the absolute difference alongside the percent, especially when the original value is small or when you are comparing changes across items with different baselines. If you are tracking trends over time, keep the same baseline definition (original versus new) across your comparisons so your percentages stay comparable.