Percentage Change Calculator

Find the percent increase or decrease between two numbers, work back to the original value before a change, and check percentage difference or percent error.

Result

+25%

Going from 120 to 150 is an increase of 25%.

Absolute change

+30

Direction

Increase

Multiplier

×1.25

As a decimal

0.25

How it was worked out

((150 − 120) ÷ 120) × 100 = 25%

Change, Both Ways Round

Working out a percentage change is easy. Working backwards from one, or knowing whether you should be measuring change at all, is where most people slip. This calculator separates those cases so the answer you get is the one your question actually needs.

Increase · Decrease · Reverse · Error

Why Use This Percentage Change Calculator?

Increase and Decrease in One Place

Enter two numbers and read the change with its sign, the absolute gap, the multiplier, and the decimal form. No guessing which formula fits which direction.

Reverse a Change

Recover the price before a discount or the figure before a rise. It divides by the multiplier rather than subtracting the percentage, which is the step most people get wrong.

Difference Kept Separate

When neither value came first, percentage difference is the right measure. It sits in its own tab with its own formula, so the two are never mixed up.

Percent Error for Lab Work

Compare a measured reading against an accepted value and get the error, the signed error, and the accuracy, which is exactly what a lab write-up asks for.

How this Percentage Change Calculator works

Every mode here rests on one idea: a percentage only means something once you know what it is a percentage of. Picking the wrong base causes nearly all percentage mistakes, so each tab fixes a different base and prints it in the formula line under your answer.

Percentage change divides by the starting value. Order matters, which is why 120 to 150 gives 25 percent while 150 to 120 gives 20 percent from the same gap of 30. When the starting value is negative, the tool divides by its absolute size, so a shrinking loss still reads as an increase.

Applying a change multiplies by 1 plus the rate. Reversing one divides by that same factor, and this is the step people get wrong. A jacket bought for 68 after 15 percent off did not start at 68 plus 15 percent. It started at 68 divided by 0.85, which is 80. Running forwards and backwards through one factor is what keeps the two answers consistent.

Percentage difference has no starting value at all, so it divides by the average of the two numbers and always returns a positive result. Percent error uses the accepted value as its base and reports two figures: the unsigned one a lab report asks for, and the signed one that tells you whether your reading came in high or low.

Answers carry up to four decimal places, and nothing is rounded before the calculation runs. Every figure is worked out in your browser.

How to use this Percentage Change Calculator

1

Pick the calculation

Change between two values, apply a percentage, work back to the original, percentage difference, or percent error. Each mode keeps its own numbers.

2

Type your two values

Decimals with a comma or a full stop both work, and negative numbers are fine. The result updates as you type, with no calculate button to press.

3

Check the formula and copy

Under the answer sit the exact arithmetic and four supporting figures, such as the absolute change, the multiplier, and the direction.

Example Usage

Measuring growth between two figures:

Input
From 120 to 150
Output
+25% — an increase of 30, a ×1.25 multiplier

Frequently Asked Questions

What is the percentage change formula?
Subtract the old value from the new value, divide by the old value, then multiply by 100. Written out: ((new − old) ÷ old) × 100. Going from 120 to 150 gives ((150 − 120) ÷ 120) × 100, which is a 25% increase. The tool prints this line under every answer with your own numbers in it.
Is percentage change the same as percentage increase?
They use the same formula. The only difference is the label: a positive result is called an increase and a negative one a decrease. Percentage change is the neutral term that covers both, which is why a single calculator handles either direction and reports the sign for you.
How do I find the original price before a discount?
Use the reverse mode. Enter the price you paid, the discount percentage, and set the toggle to decrease. A jacket bought for $68 after 15% off started at $80, because 68 ÷ 0.85 = 80. Subtracting 15% from the sale price is the classic mistake here and gives $57.80, which is wrong.
Which number goes in the "from" box?
The one that came first in time. Percentage change is measured against the starting value, so swapping the two boxes changes the answer. From 120 to 150 is a 25% rise, but 150 to 120 is a 20% fall, even though the gap is 30 either way. If neither value came first, use percentage difference instead.
What is the difference between percentage change and percentage difference?
Change needs a starting point and measures movement away from it. Difference treats both numbers as equals and divides by their average, so the order does not matter. Comparing 40 and 60 gives a 50% change if 40 came first, but a 40% difference. Use change for before-and-after data and difference for two independent readings.
How do I calculate percent error?
Take the difference between your measured value and the accepted value, drop the minus sign, divide by the accepted value, and multiply by 100. The error mode does this and also shows the signed version, so you can see whether your reading came in high or low. That direction usually matters more in a lab report than the size alone.
Can I use negative numbers?
Yes. When the starting value is negative, the tool divides by its absolute size so the sign of the result still describes the direction of travel. A move from −50 to −30 reads as a 40% increase, which matches how a loss shrinking is normally described.
Why does a 50% rise need only a 33% fall to undo it?
Because each percentage is taken from a different base. 100 rising by 50% reaches 150, and getting back to 100 means losing 50 out of 150, which is 33.33%. This is why investment losses hurt more than equivalent gains help, and it is worth checking both directions in the calculator before quoting a figure.
What does a change of more than 100% mean?
The value more than doubled. Growing from 40 to 100 is a 150% increase, because the gain of 60 is one and a half times the starting figure. A decrease, on the other hand, cannot go past 100% unless the value turns negative, since you cannot lose more than all of something.
How many decimal places does it show, and is my data private?
Results carry up to four decimal places with trailing zeros removed, and nothing is rounded before the calculation runs. Every figure is worked out in your browser, so nothing you type leaves your device, the tool needs no account, and it keeps working offline once the page has loaded.

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