What it means
Many businesses have a natural yearly rhythm, such as a retailer's busy December or a tax adviser's busy spring. Comparing December sales with November sales would mix the effect of the season with the effect of performance.
Comparing this December with last December removes most of the seasonal distortion, which is why the YoY comparison is so common. The calculation is simple, which helps it spread through business conversations.
Take the current figure, subtract the figure from the same period last year, and divide by last year's figure. Companies use it for revenue, profit, customer numbers, costs and almost every other measure.
It is often paired with the sequential comparison, which compares one period with the one immediately before. Sequential figures show momentum, while YoY figures show the underlying trend over the full cycle.
A business growing 20% year-over-year but shrinking quarter-on-quarter may be losing steam. Care is needed with the base.
A small figure last year can make a modest increase look spectacular, and a large figure last year can make a decent result look weak. If last year's period contained a one-off event, such as an acquisition, a strike or a particularly unusual contract, the comparison may need adjusting.
Calendar quirks also matter. A leap year, a different number of trading days or a holiday that moves between periods can distort a YoY comparison.
Good reports state when they have adjusted for these differences so readers can judge the numbers fairly. The same logic works for costs, margins and cash flow, not only revenue.
A company can use YoY change to see whether expenses are growing faster than sales, which would squeeze profit even when revenue looks healthy. Pairing the two comparisons in one table makes that pattern easy to spot.
In practice
Real-world examples.
Example
A retailer reports that December sales were $4,200,000, compared with $3,500,000 the previous December. The finance team calculates YoY growth of 20% and reports it to the board. They compare it with an industry growth of 8% to show the company is gaining share. The board also asks for a breakdown by product, so that growth from new lines is separated from growth in existing ones.
Example
A subscription business tracks monthly active customers and finds the number is up 12% year-over-year, but down slightly from last month. Management concludes that the underlying trend is positive while recent momentum has slowed. They investigate whether a recent price rise has affected sign-ups. The team will review the figures again next month before drawing a firm conclusion.
Example
A hotel group compares this summer's occupancy with last summer's and sees a 5-point drop. Before alarming the board, the analyst checks that last summer included a major conference that does not repeat. Adjusting for the event shows occupancy is broadly flat.
Formula
Calculation
YoY change (%) = (current period - same period last year) / same period last year x 100
Suppose a software company reported quarterly revenue of $12,500,000 this year against $10,000,000 in the same quarter last year. The change = 12,500,000 - 10,000,000 = $2,500,000. YoY growth = 2,500,000 / 10,000,000 x 100 = 25%. If costs rose from $8,000,000 to $9,200,000 over the same period, the cost change is 1,200,000 / 8,000,000 x 100 = 15%, so revenue grew faster than costs.Case study
Seen in the real world.
Pinecrest Outdoor Gear is an illustrative, fictional retailer with strong winter sales. Its monthly report showed that January sales were 30% lower than December, and the new finance manager worried about a collapse.
She changed the report to show year-over-year change alongside the monthly figures. January this year was $1,800,000 against $1,500,000 the previous January, a YoY increase of 20%, so the business was growing and the fall from December was simply seasonal.
She also added a note on the number of trading days and a weather adjustment, so that the board could see how much of the change came from conditions rather than from performance. After three months, directors stopped asking about month-on-month drops and began asking about the year-over-year trend. The illustrative lesson is that the right comparison turns an alarming number into an accurate story.
Watch out
Common mistakes.
- Comparing a month with the previous month in a seasonal business, when the same month last year is the fairer comparison.
- Ignoring an unusually small or unusually large base period, which can exaggerate or hide real growth.
- Confusing percentage points with percentages, when a margin rising from 10% to 12% is up 2 percentage points but 20% in relative terms.
Questions
People also ask.
What is year-over-year?
It is a comparison of a period with the same period in the previous year, usually shown as a percentage change.
How is YoY different from quarter-on-quarter?
Quarter-on-quarter compares with the previous quarter, while YoY compares with the same quarter a year ago and removes seasonality.
Why do investors focus on YoY growth?
It gives a clean measure of trend that is not distorted by seasons, so it is easier to compare companies.
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