Year-over-year (YoY) percentage change compares a value in one period to the same period one year earlier — for example, this March compared to last March, or Q2 this year compared to Q2 last year. It uses the same percentage change formula as any other comparison, just applied specifically to same-period, year-apart values.

YoY change = (This year's value - Last year's value) / Last year's value × 100

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Why YoY instead of month-over-month?

Comparing consecutive months (like March to April) can be misleading for businesses with seasonal patterns — a toy store's April revenue will naturally differ from its December revenue regardless of whether the business is actually growing. Comparing March this year to March last year removes that seasonal noise and shows the underlying trend.

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Worked example: quarterly revenue

A company's Q2 revenue was $840,000 last year and $945,000 this year. What is the YoY percentage change?

Step 1: Last year's value = 840,000, this year's value = 945,000
Step 2: (945,000 - 840,000) / 840,000 × 100 = 105,000 / 840,000 × 100 = 12.5
Step 3: Revenue grew 12.5% year-over-year in Q2.

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A note on comparing percentages

If you're comparing two YoY growth rates themselves (say, 12.5% this quarter vs. 9% the quarter before), remember that the difference between them is measured in percentage points, not percent.

Ready to run your own numbers? Use the percentage change calculator with last year's and this year's figures.