What is a Percentage Change Calculator?
Percentage change trips people up because the base matters: going 100→150 is +50%, but 150→100 is −33%, not −50%.
Enter the old and new values; the tool applies change ÷ old × 100 and labels the direction for you.
Picking the base is the whole job, and each common case has its own: budget against actual uses the budget, year on year uses last year, before and after uses before. One behaviour worth knowing here: the tool divides by the absolute old value, so a loss narrowing from −200 to −100 reads as a 50% increase. The magnitude is right; the direction word follows the arithmetic, not the business meaning.
Frequently asked questions
Why does a 50% drop need a 100% gain to break even?
Because the base shrinks with the fall. Going 100 → 50 is −50%, but climbing back from 50 to 100 is +100% on the new, smaller base. Every decline needs a larger percentage to undo it, which is why a holding down 50% is nowhere near halfway home.
Percentage change or percentage difference: which do I want?
Change has a direction and a fixed base, the old value, and is what this tool computes. Difference is symmetric: the gap divided by the average of the two numbers, for when neither came first. Before-and-after wants change; two readings of the same thing want difference.
What is the formula?
(new − old) ÷ |old| × 100. The old value is always the base.
Why is 100→150 +50% but 150→100 −33%?
Because the base changes: +50 on a base of 100, −50 on a base of 150.
What if the old value is 0?
Percentage change from zero is mathematically undefined: the tool asks for a non-zero base.
Percentage change vs percentage points?
10%→15% is a +50% relative change but +5 percentage points. Say “points” when comparing two percentages.