Percentage Change Calculator
Enter two numbers to get the percentage increase or decrease between them, with each step of the working shown.
The calculator never sends or saves what you type.
Neither number the starting point? Percentage difference calculator.
On this page
The percentage change formula
Change % = (Ending − Starting) ÷ Starting × 100
The divisor is always the starting value — the number the change is measured against. Dividing by the ending value instead is the usual mistake, and it gives a different answer in both directions.
Percentage increase and decrease
They are one calculation, not two. The sign of the answer carries the direction, so the same formula covers a price rise and a discount. If you only ever deal in rises — pay, rent, prices — the percentage increase calculator frames the same arithmetic that way round; for cuts and depreciation, the percentage decrease calculator; for body weight, the weight loss percentage calculator.
| Starting | Ending | Working | Change |
|---|---|---|---|
| 80 | 104 | 24 ÷ 80 × 100 | +30% |
| 200 | 175 | −25 ÷ 200 × 100 | −12.5% |
| 2,400 | 3,000 | 600 ÷ 2,400 × 100 | +25% |
| 43 | 43 | 0 ÷ 43 × 100 | 0% |
The mistake worth knowing
A percentage rise and an equal percentage fall do not cancel out. £100 up 20% is £120; £120 down 20% is £96.
Each percentage is taken from its own starting value, and the second one is larger. The gap widens as the percentage grows: a 50% rise then a 50% fall leaves you at 75% of where you began.
Percent or percentage points?
If a rate moves from 10% to 15%, that is a rise of 5 percentage points and a 50% increase. Both are correct and they describe different things. Use points when comparing two percentages to each other, and percent when measuring how much one number grew relative to itself.
An alert threshold is the same distinction. A rule that fires when an error rate passes 1% is a point on the rate, not a 1% rise in it: an error rate that moves from 0.5% to 0.75% is up 50% and still 0.25 points below the line. OpsCanopy’s Loki alert rule tester runs a rule against sample logs before it pages anyone.
Percentage change or percentage difference?
Percentage change has a direction: it measures a move from a starting value, so swapping the two numbers changes the answer. Percentage difference has none. It compares two numbers where neither is the reference — two quotes for the same job, two measurements of the same thing — and divides the gap by their average instead. It is meant for two positive numbers: with mixed signs the average stops being a fair yardstick.
Difference % = |a − b| ÷ ((a + b) ÷ 2) × 100
Take 40 and 60. The gap is 20 and the average is 50, so the percentage difference is 20 ÷ 50 × 100 = 40%, in either order. As a change, the same pair gives two answers: 40 to 60 is +50% (20 ÷ 40), and 60 to 40 is −33.33% (−20 ÷ 60).
The calculator above computes percentage change. For the symmetric figure, the percentage difference calculator works any pair through with the gap, the average and a check. Percent error is a third relative of both: a result against a known correct value, |measured − accepted| ÷ |accepted| × 100 — the percent error calculator does that one, with the signed and absolute error.
What percent is one number of another?
A related question — not how much something moved, but how big one number is next to another at the same moment. Divide the part by the whole and multiply by 100 — 45 of 180 is 45 ÷ 180 × 100 = 25%, and the remaining 135 is the other 75%. For exam marks, the marks percentage calculator does this interactively.
The number you divide by is the one after the word "of". Both orders compute, but only one answers the question you asked: 180 of 45 returns 400%, which is true and almost never what was meant. An answer above 100% is the honest signal that the part and the whole have been swapped — unless the part genuinely exceeds the whole, as revenue against a smaller target does.
Going the other way
This page answers "what percentage change happened?" when you know both numbers. If you know the percentage and the number after the change, and you want the value before it, that is the reverse calculation — use the reverse percentage calculator. If you know a number and a percentage and simply want that percentage of it, the same tool does that too.
One neighbour is easy to confuse with this page: X is Y% of what number? starts from a part and a percentage and returns the whole. This page starts from two values and returns a change. Same three quantities, different unknown.
Frequently asked questions
How do you calculate percentage change between two numbers?
Subtract the starting value from the ending value, divide by the starting value, then multiply by 100. From 80 to 104: 104 − 80 = 24, then 24 ÷ 80 = 0.3, then × 100 = a 30% increase.
Is percentage increase the same calculation as percentage decrease?
Yes — it is one formula, and the sign tells you the direction. A negative answer is a decrease. That is why this page handles both: 200 to 175 gives −12.5%, which reads as a 12.5% decrease.
Why is a 20% rise followed by a 20% fall not back where you started?
Because each percentage is taken from a different base. £100 rising 20% is £120; £120 falling 20% is £96, not £100. The fall was 20% of the larger number. This is the single most common percentage error, and it is why reversing a change needs division rather than subtraction.
What is the percentage change if the starting value is zero?
There is not one. Percentage change measures a difference relative to the starting value, and nothing is relative to zero — any rise from 0 would be infinitely large. The calculator says so rather than printing a misleading number.
What if the starting value is negative?
The change is measured against the size of the starting value, so −50 to −25 reads as a 50% increase. Keeping the minus sign in the divisor would return −50% and describe a rise as a fall. The calculator shows a note whenever it does this, so the working is never hidden.
What percent is one number of another?
Divide the part by the whole and multiply by 100: 45 of 180 is 45 ÷ 180 × 100 = 25%. That is a different question from the one this page answers — it compares two things at the same moment rather than measuring a move from one to the other.
What is the difference between percent and percentage points?
A move from 10% to 15% is a rise of 5 percentage points, but a 50% increase. Points measure the gap between two percentages; percent measures relative change. Mixing them up overstates or understates a change badly, and it is common in reporting.
What is the difference between percentage change and percentage difference?
Percentage change measures a move from a starting value, so the order matters: 40 to 60 is a 50% increase, but 60 to 40 is a 33.33% decrease. Percentage difference compares two numbers with neither as the reference — it divides the gap by their average, |a − b| ÷ ((a + b) ÷ 2) × 100, so 40 and 60 differ by 40% whichever comes first. This calculator computes percentage change; the percentage difference calculator works out the symmetric one.