How do I calculate a percentage increase?

New value minus original value, divided by the absolute value of the original, times 100. From 1,200 to 1,320 is (1,320 − 1,200) ÷ |1,200| × 100 = 10%, so a 10% increase. Enter the two values and the result is labelled as an increase.

How do I calculate a percentage decrease?

The same formula, with the new value lower than the original, which makes the answer negative. From 800 to 680 is (680 − 800) ÷ 800 × 100 = −15%, a 15% decrease. The calculator labels it as a decrease and shows the minus sign.

What is the difference between an increase and a decrease?

Only the direction, and therefore the sign. A positive result means the value went up; a negative result means it went down. The calculator names which one it is above the figure.

Is percentage change the same as percentage difference?

No. Percentage change has a before and an after, and measures against the earlier value — that is what this calculator does. Percentage difference compares two values with no order between them, usually against their average, and carries no sign. If your numbers are a before and an after, percentage change is the right one.

Why isn't a rise and a fall of the same amount the same percentage?

Because percent change is relative to the starting value. Going from 150 to 180 is +20%, but going from 180 to 150 is −16.67%, since the starting points differ.

Why can't the original value be zero?

Percent change is measured relative to the absolute value of the original value, and dividing by zero has no defined result — a rise from nothing is not 100% or any other percentage. Enter a non-zero original value, or describe the move in plain units instead.

Does it handle negative numbers?

Yes, using one stated convention: the denominator is the absolute value of the original number, |old|. Moving towards a larger number is therefore always an increase — −100 to −80 is +20%, and −80 to −100 is −25%. Tools that divide by the signed value report the opposite sign on a negative baseline, so figures from elsewhere may not match.

What if the values cross zero?

The calculator still returns a number — −50 to 50 gives +200% — but a percentage change stops being a useful description once the quantity changes sign. Use the absolute change instead, which is +100 in that example.

Results are shown rounded to two decimals. The calculation behind them uses full precision.

Can I share a calculation?

Yes. Use Share to copy a link that reopens the calculator with the same two values.

Percent change calculator

Enter the original value and the new value. The calculator names the direction — percentage increase or percentage decrease — and shows the percentage and the absolute difference as you type.

Written by Kenneth Schrøder, Founder of WiseCalcs

Updated September 8, 2026

It calculates (new − original) ÷ |original| × 100. Using the absolute value of the original keeps the sign tied to the direction of the move, including when the starting value is negative.

Original value

New value

Higher than the original value is an increase; lower is a decrease.

Percentage increase

+20%

Signed change: +30

The headline says which direction the move was — a percentage increase or a percentage decrease — and the signed figure gives its size. Underneath is the absolute change in plain units, and the bars compare the two values so a large percentage on a small base is not mistaken for a large move.

How does it work?

A positive result is an increase, a negative result is a decrease. Dividing by |old| rather than the signed value is a deliberate convention: it makes a move towards a larger number positive whatever the signs, so -100 to -80 is +20% and -80 to -100 is -25%. Tools that divide by the signed value report the opposite sign on a negative baseline. Two limits follow: when the values sit on opposite sides of zero the percentage is defined but no longer describes proportional growth (-50 to 50 is +200%), and a starting value of zero has no percentage change at all.

Percent change formula

\frac{\text{new} - \text{old}}{\lvert \text{old} \rvert} \times 100

old: The original value you are comparing from. The denominator is its absolute value |old|, so the sign of the result follows the direction of the move, not the sign of the baseline.
new: The new value you are comparing to.

From 150 to 180 is (180 − 150) ÷ 150 × 100 = +20%.

Method & sources

Inputs are treated as plain numbers without units or currency. Percentage change divides by the absolute value of the starting value, |old|, not by the signed value. A move towards a larger number is therefore always positive: -100 to -80 is +20%, and -80 to -100 is -25%.

How we calculate

Inputs are treated as plain numbers without units or currency.
Percentage change divides by the absolute value of the starting value, |old|, not by the signed value. A move towards a larger number is therefore always positive: -100 to -80 is +20%, and -80 to -100 is -25%.

Limitations

The |old| convention is a choice. Tools that divide by the signed starting value report the opposite sign whenever the starting value is negative, so -100 to -80 reads as -20% there and +20% here. Neither is wrong; check which one a figure came from before comparing.
When the two values sit on opposite sides of zero, the percentage is still defined but stops describing proportional growth: -50 to 50 comes out as +200%, which says little about a quantity that changed sign. Read the absolute change instead.
A starting value of zero has no percentage change at all, because the formula would divide by zero. The calculator asks for a non-zero starting value rather than showing an infinity.

Rounding

Results are rounded to two decimals for display. The calculation itself uses full precision.

What this calculator does

Percent change tells you how much a value grew or shrank relative to where it started. This calculator takes an original value and a new value and gives you both the percentage and the plain difference between them. There is nothing to switch: a rise comes back as a percentage increase, a fall as a percentage decrease, and the calculation behind the two is identical.

Percentage increase

Subtract the original value from the new one, divide by the absolute value of the original, and multiply by 100. For a positive starting value this is the familiar formula. A rent of 1,200 that becomes 1,320 rises by 120; 120 ÷ 1,200 = 0.1, so it is a 10% increase. Enter 1,200 and 1,320 and the result reads +10% with an absolute change of +120.

Percentage decrease

Exactly the same arithmetic, with the new value below the original, so the answer comes out negative. A laptop cut from 800 to 680 falls by 120; −120 ÷ 800 = −0.15, so it is a 15% decrease. Enter 800 and 680 and the result reads −15% with an absolute change of −120. The minus sign is the only thing that distinguishes a decrease from an increase here.

How to use it

Enter the original value — where the number started.
Enter the new value — where it ended up.
Read the percent change and the absolute change below.

Why a rise and a fall are not mirror images

The percentage always measures against the starting value, and the starting value changes when you reverse the direction. A subscription going from 150 to 180 rises by 30 on a base of 150, which is +20%. Coming back down from 180 to 150 falls by the same 30, but now on a base of 180, which is only −16.67%. That is also why a 20% increase followed by a 20% decrease does not return you to where you began: 150 → 180 → 144.

Percentage change or percentage difference?

They are different questions. Percentage change has a direction: one value came first, the other came after, and the earlier one is the baseline — that is what this calculator computes. Percentage difference compares two values with no before and after, so it is usually measured against their average and has no sign; 150 and 180 differ by 18.18% of their average, whichever order you name them in. If your two numbers are a before and an after, percentage change is the one you want. This page does not calculate percentage difference.

Negative values: which convention this uses

Once the starting value can be negative, the formula needs a decision, because there are two defensible denominators. This calculator divides by the absolute value of the original number, |old|. That is a choice, not the only correct answer, and it is worth knowing which one you are reading.

The sign shows whether the number increased or decreased. From −100 to −80, the increase is 20 relative to a starting magnitude of 100, giving +20%. From −80 to −100, the decrease is 20 relative to 80, giving −25%. Whether an increase is good or bad depends on what the numbers represent. A calculator that divides by the signed starting value would give −20% for the first example, so check the formula before comparing results.

If the values are on opposite sides of zero, the formula still returns a number: −50 to 50 gives +200%. That percentage can be misleading as a description of growth; report the starting and ending values and the change of +100 as well. A starting value of zero is not supported because the formula would divide by zero.

Common mistakes

Swapping the original and new values. The original is the value you compare against.
Reading the percentage as the new total. A +20% change on 150 is an increase of 30, ending at 180.
Expecting a fall and a rise of the same size to use the same percentage. Going 150 → 180 is +20%, but 180 → 150 is −16.67%, because the starting points differ.

Where to go next

This page covers one case: old value to new value. If you also need a percentage of a number, or one number as a percentage of another, the percentage calculator covers all three questions in one place. For a price reduction where you want the new price rather than the percentage, use the discount calculator, and for a percentage added to a restaurant bill and split between people, the tip calculator.

When it's useful

Price rises, salary changes, traffic and growth metrics, before-and-after comparisons, and any time you need to express a difference as a percentage.

FAQ

How do I calculate percent change?: Subtract the original value from the new value, divide by the absolute value of the original, and multiply by 100. From 150 to 180 is (180 − 150) ÷ |150| × 100 = 20%.
How do I calculate a percentage increase?: New value minus original value, divided by the absolute value of the original, times 100. From 1,200 to 1,320 is (1,320 − 1,200) ÷ |1,200| × 100 = 10%, so a 10% increase. Enter the two values and the result is labelled as an increase.
How do I calculate a percentage decrease?: The same formula, with the new value lower than the original, which makes the answer negative. From 800 to 680 is (680 − 800) ÷ 800 × 100 = −15%, a 15% decrease. The calculator labels it as a decrease and shows the minus sign.
What is the difference between an increase and a decrease?: Only the direction, and therefore the sign. A positive result means the value went up; a negative result means it went down. The calculator names which one it is above the figure.
Is percentage change the same as percentage difference?: No. Percentage change has a before and an after, and measures against the earlier value — that is what this calculator does. Percentage difference compares two values with no order between them, usually against their average, and carries no sign. If your numbers are a before and an after, percentage change is the right one.
Why isn't a rise and a fall of the same amount the same percentage?: Because percent change is relative to the starting value. Going from 150 to 180 is +20%, but going from 180 to 150 is −16.67%, since the starting points differ.
Why can't the original value be zero?: Percent change is measured relative to the absolute value of the original value, and dividing by zero has no defined result — a rise from nothing is not 100% or any other percentage. Enter a non-zero original value, or describe the move in plain units instead.
Does it handle negative numbers?: Yes, using one stated convention: the denominator is the absolute value of the original number, |old|. Moving towards a larger number is therefore always an increase — −100 to −80 is +20%, and −80 to −100 is −25%. Tools that divide by the signed value report the opposite sign on a negative baseline, so figures from elsewhere may not match.
What if the values cross zero?: The calculator still returns a number — −50 to 50 gives +200% — but a percentage change stops being a useful description once the quantity changes sign. Use the absolute change instead, which is +100 in that example.
Are results rounded?: Results are shown rounded to two decimals. The calculation behind them uses full precision.
Can I share a calculation?: Yes. Use Share to copy a link that reopens the calculator with the same two values.

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