Year-over-year (YoY) growth is simply the percentage change between the same metric in two periods one year apart: (this year - last year) / last year x 100. If revenue rose from $120,000 to $150,000, that is (150,000 - 120,000) / 120,000 x 100 = a 25% YoY increase.
It is the most common growth number in business reporting - but it is easy to read it wrong, especially when several years are involved or when the metric is itself a rate. Here is how to calculate YoY correctly, where it misleads, and when to switch to a smoothed multi-year rate instead.
The YoY formula, step by step
YoY growth is a percentage change calculation, nothing more:
- Subtract last year's value from this year's value.
- Divide by last year's value (the base period).
- Multiply by 100 to express it as a percent.
A negative result is a decline. From $150,000 down to $135,000 the next year: (135,000 - 150,000) / 150,000 x 100 = -10% YoY. The base is always the earlier period - swapping the order flips the sign and the size, which is a frequent error. You can confirm any pair instantly in the percentage change calculator.
Worked example: a four-year revenue path
Suppose a small business reports these year-end revenues:
| Year | Revenue | YoY change |
|---|---|---|
| Year 0 | $100,000 | - |
| Year 1 | $150,000 | +50.00% |
| Year 2 | $135,000 | -10.00% |
| Year 3 | $200,000 | +48.15% |
Each YoY figure is an honest percentage change for that one year. But here is the trap: the simple average of those three YoY rates is (50 - 10 + 48.15) / 3 = 29.38% per year - and that number is wrong as a description of overall growth.
Why averaging YoY rates overstates growth
Averaging percentage changes ignores that each year compounds on a different base, the same reason an up-and-down swing never nets to zero. The honest annualized rate is the compound annual growth rate (CAGR), which finds the single steady rate that turns $100,000 into $200,000 over three years:
CAGR = (200,000 / 100,000)1/3 - 1 = 25.99% per year.
So the true smoothed growth was about 26% a year, not the 29.38% you get by averaging the YoY figures. The simple average overstated it by more than three percentage points, because it gave the big +50% and +48% years equal weight without accounting for the down year compounding underneath. For multi-year growth, lean on the CAGR calculator, not an average of annual changes.
The percentage-points trap when the metric is a rate
YoY gets especially slippery when the thing you are tracking is itself a percentage - a margin, an interest rate, an unemployment rate. Moving from 3% to 4.5% is a rise of 1.5 percentage points, but as a percentage change it is (4.5 - 3) / 3 x 100 = a 50% relative increase. Both statements are true; they answer different questions.
| Rate change | Percentage points | Relative % change |
|---|---|---|
| 5% to 6% | +1.0 point | +20% |
| 3% to 4.5% | +1.5 points | +50% |
| 2% to 4% | +2.0 points | +100% |
When you report a margin that went "up 50%," be clear whether you mean 50% of the old margin (relative) or 50 percentage points (a far bigger move). Mixing the two is how a modest shift gets dressed up as a dramatic one. For finding a percentage of a single value rather than the change between two, use the percentage calculator.
When to use YoY vs CAGR
- Use YoY to compare two specific periods - this quarter vs the same quarter last year, this year vs last - and to spot the most recent direction and seasonality.
- Use CAGR when you want one number that summarizes a trend across three or more years, smoothing out the bumpy individual years.
- Never average YoY rates to describe a multi-year period - it overstates growth whenever the path is uneven.
YoY answers "how fast did it change this year," while CAGR answers "what steady annual rate would have produced this result." If you are projecting forward from a growth rate, plug your CAGR into the investment calculator rather than the noisiest recent YoY figure.
Putting it together
For any single period-over-period comparison - revenue, traffic, prices, headcount - YoY is the right, simple tool, and it is exactly a percentage change. The moment you stretch across several years, switch to CAGR; the moment your metric is itself a rate, separate percentage points from relative change. For a deeper look at why CAGR beats a plain average, see CAGR vs average annual return.
For official guidance on how growth rates are defined and reported, the U.S. Bureau of Labor Statistics' Consumer Price Index program is a reliable, ad-free reference on percentage-change reporting.
Try it yourself
Run your own numbers in the free Percentage Change Calculator — instant, private, no sign-up.
Open the Percentage Change Calculator →Frequently asked questions
- What is the formula for year-over-year growth?
- Year-over-year growth equals (this year's value - last year's value) / last year's value x 100. If sales went from $120,000 to $150,000, YoY growth is (150,000 - 120,000) / 120,000 x 100 = 25%. The earlier year is always the base, or denominator.
- Why can't I just average my yearly percentage changes?
- Averaging YoY rates overstates real growth whenever the path is uneven, because each year compounds on a different base. For revenue of $100,000 growing to $200,000 over three years, the simple average of the YoY changes is 29.38% per year, but the true compound rate (CAGR) is only 25.99% per year.
- Should I use YoY or CAGR?
- Use YoY to compare two specific periods one year apart and to see the latest direction. Use CAGR when you want a single smoothed annual rate across three or more years. YoY shows the recent change; CAGR shows the steady rate that would produce the overall result.
- What is the difference between percentage points and percent change for a rate?
- Percentage points measure the raw gap between two rates, while percent change measures the gap relative to the starting rate. A move from 3% to 4.5% is a rise of 1.5 percentage points but a 50% relative increase, since 1.5 divided by 3 is 0.50.
- How do I handle a negative year-over-year change?
- A negative YoY result simply means the value declined, and you read the magnitude as the size of the drop. From $150,000 to $135,000, YoY is (135,000 - 150,000) / 150,000 x 100 = -10%, a 10% decrease for that year.
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