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Percent Change Calculator: Increase or Decrease, With Working

Percent increase or decrease from an old value to a new one, with the working and the change back.

Inputs

Percent change
38.46% increase

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What each Percent Change input means

From (original)
The original or old value — the base the change is measured against. It cannot be 0. A negative starting value is divided by its size, so the direction of the change stays right.
To (new value)
The new value. Anything goes, including 0 (a 100% decrease) and values more than double the original (an increase of over 100%).

Percent Change formula

percent change = (new − original) ÷ |original| × 100

%Δ=new−original∣original∣×100\%\Delta = \frac{\text{new} - \text{original}}{|\text{original}|} \times 100

OpenStax Prealgebra sets it out in two steps: find the amount of the change (new minus original), then find what percent of the original amount that change is. A positive answer is an increase, a negative one a decrease. The base is always the original value, which is why a change and its reverse are different percentages: a rise from 26 to 36 is 38.46%, but the fall from 36 back to 26 is 27.78%, because 10 is a smaller share of 36. The page shows both, the multiplier (new ÷ original), and the working. When the original is negative — a loss, a temperature below zero — the change is divided by its size, so a move from −50 to −25 reads as an increase.

Percent Change worked example

OpenStax's own example: a fee rising from 26 to 36 a unit. The change is 36 − 26 = 10, and 10 ÷ 26 × 100 = 38.46% — a 38.5% increase. Going back down from 36 to 26 would be a 27.78% decrease, because the base is now 36.

More Percent Change examples

Rent falling from 1,200 to 900 a month: (900 − 1,200) ÷ 1,200 × 100 = −25%, which the page reports as a 25.00% decrease. Getting back from 900 to 1,200 would take a 33.33% increase, because 300 is a bigger share of 900.

A gallon of milk going from 3.49 to 3.99: the change is 0.50, and 0.50 ÷ 3.49 × 100 = 14.33% increase. The multiplier, 1.1433, is the same fact in one number: new price = old price × 1.1433.

Where the Percent Change calculator can give the wrong answer

  • The original value cannot be zero: any change from zero is an infinite percentage, so the page returns an error.
  • Percent change is not the same as percentage points. A rate going from 4% to 6% is a 2-point rise but a 50% increase.
  • A change and its reverse differ: down 25% from 100 is 75, and getting back to 100 needs 33.33% up.
  • With a negative original value the change is divided by its absolute value, so moving towards zero (−50 to −25) is an increase. Some textbooks divide by the signed value instead and call that a decrease; check which your course uses.

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Percent Change reference table

A rise and the fall that undoes it, and the other way round
PercentUp by this, then back down byDown by this, then back up by
5%4.76%5.26%
10%9.09%11.11%
20%16.67%25%
25%20%33.33%
33.33%25%50%
50%33.33%100%
75%42.86%300%
100%50%— (nothing is left)
Source: Arithmetic: after a rise of p, the fall back is p ÷ (1 + p); after a fall of p, the rise back is p ÷ (1 − p)

Percent Change FAQ

A 40% increase: (7 − 5) ÷ 5 × 100 = 2 ÷ 5 × 100 = 40%.