How to Calculate Percentage Change (With Examples)

Prices go up, traffic goes down, a salary changes. Percentage change turns those differences into a number you can compare. The formula is short, but it's easy to use the wrong base.

The formula

Percentage change = (new value − old value) ÷ old value × 100

• A positive result is an increase.
• A negative result is a decrease.

Worked examples

Price increase. A product went from 80 to 100.

(100 − 80) ÷ 80 × 100 = 20 ÷ 80 × 100 = 25% increase

Decrease. Website visits dropped from 1,200 to 900.

(900 − 1,200) ÷ 1,200 × 100 = −300 ÷ 1,200 × 100 = −25%, a 25% decrease

Salary. 52,000 to 54,600.

2,600 ÷ 52,000 × 100 = 5% raise

If you'd rather not do the arithmetic, the percentage calculator has a "% change from A to B" mode that shows each step.

Mistake 1: Dividing by the wrong value

The base is always the starting value. From 80 to 100 is +25%, but from 100 back to 80 is −20%, because the second change is measured against 100.

Mistake 2: Expecting changes to cancel out

A stock falls 50% and then rises 50%. Is it back where it started? No:

• 100 − 50% = 50
• 50 + 50% = 75

To undo a 50% drop you need a 100% increase. In general, to undo a decrease of d%, you need an increase of d ÷ (100 − d) × 100 percent.

Mistake 3: Percent vs. percentage points

When an interest rate goes from 4% to 6%:

• It rose by 2 percentage points (6 − 4).
• It rose by 50 percent ((6 − 4) ÷ 4 × 100).

Both statements are correct, but they're not interchangeable. News reports about rates, polls and unemployment should use percentage points for the absolute difference.

Related calculations

Increase a number by a percentage: new = old × (1 + p/100). 80 increased by 25% is 80 × 1.25 = 100.

Decrease by a percentage: new = old × (1 − p/100). A 30% discount on 60 is 60 × 0.7 = 42.

Find the original before a percentage was added. A price of 119 includes 19% tax. The original is 119 ÷ 1.19 = 100, not 119 − 19% (which would be 96.39).

Percentage difference between two values (when neither is the "old" one) uses the average as base: |a − b| ÷ ((a + b) ÷ 2) × 100. This is used for comparing two measurements rather than a change over time.

Quick reference

Question	Formula
What is p% of x?	x × p ÷ 100
x is what % of y?	x ÷ y × 100
Change from a to b	(b − a) ÷ a × 100
Original before +p%	value ÷ (1 + p/100)

For longer calculations with powers or roots, the scientific calculator keeps a history you can reuse.

Percentage change in spreadsheets

In Excel or Google Sheets, with the old value in A2 and the new value in B2:

=(B2-A2)/A2

Format the cell as a percentage. Wrap it in IFERROR(...,"") if the old value can be zero, because division by zero has no meaningful percentage change.