Year over year (YoY)
A comparison of a figure with the same period one year earlier, which removes seasonal effects.
Year over year, or YoY, compares a value with the same period one year earlier. Because it compares like with like, it removes most seasonal effects that distort month-to-month or quarter-to-quarter comparisons. A YoY growth rate is the change divided by the prior year's value.
On our site, most growth figures are shown as YoY unless labeled otherwise. Check that the base period is comparable, especially after acquisitions or calendar shifts.
Traders care because YoY shows the underlying trend in demand, especially for retailers and consumer data with strong seasonal patterns.
Worked example (illustrative numbers, not real data): retail sales in December are 80 billion dollars, against 75 billion in the same month last year. The YoY growth is 6.7 percent. The month-over-month change can look different because the holiday season falls on a different base.