Percentage Change Calculator
Calculate the percentage increase or decrease between two numbers, with the formula and direction shown.
What is X% of Y?
Quick Reference
About the Percentage Change Calculator
Percentage change is how we describe growth and decline in a way that is fair to compare across different sizes. A £10 rise means very different things on a £20 item and a £2,000 item; expressing it as a percentage — 50% versus 0.5% — captures that instantly. This percentage change calculator takes a starting value and an ending value and tells you the exact percentage increase or decrease between them.
The formula is straightforward but easy to fumble: subtract the old value from the new value, divide by the old value, and multiply by 100. The key detail is that you always divide by the original (starting) figure, not the new one — dividing by the wrong base is the classic error. The calculator handles this for you and shows the working, including whether the result is an increase or a decrease.
It is useful anywhere you need to quantify movement: price rises, salary changes, investment returns, traffic or sales growth, weight change, or year-over-year comparisons. Because it shows direction and magnitude together, you get an answer you can quote with confidence. Everything is calculated locally and privately.
Looking for more options? Open the full Percentage Calculator — it’s the same tool with every feature.
Frequently Asked Questions
How do I calculate percentage change?
Subtract the original value from the new value, divide the result by the original value, then multiply by 100. For example, from 40 to 52: (52 − 40) ÷ 40 × 100 = 30% increase. The calculator shows this working for any pair of numbers.
Why do I divide by the original value, not the new one?
Percentage change measures movement relative to where you started, so the starting (original) value is the base. Dividing by the new value gives a different, incorrect figure. This is the most common percentage-change mistake — the calculator always uses the correct base for you.
How is a percentage decrease shown?
When the new value is lower than the original, the change is negative — a percentage decrease. For example, from 50 to 40 is a 20% decrease. The calculator labels the result as an increase or decrease so the direction is never ambiguous.
Understanding Percentage Change
The formula explained
Percentage change is the difference between two values expressed relative to the starting value: (new − old) ÷ old × 100. The result tells you how much something grew or shrank in proportional terms, which lets you compare changes across very different sizes fairly. The single most important detail is that the denominator is always the original value — the point you are measuring change from.
Why increases and decreases are not symmetric
A common surprise is that a percentage increase and the equal-looking decrease do not cancel. If a £100 item rises 50% to £150, a later 50% fall takes it to £75, not back to £100 — because the second percentage is calculated from the higher £150 base. This asymmetry matters in investing and pricing: recovering from a 50% loss requires a 100% gain, not another 50%.
Percentage change versus percentage points
When the values themselves are percentages — say an interest rate moving from 4% to 6% — there are two correct ways to describe it. It is a rise of 2 percentage points (a simple subtraction) and also a 50% increase (2 ÷ 4 in relative terms). Reports often blur these, so being precise about which you mean avoids a genuinely large misunderstanding.