What Is Year-Over-Year (YoY)? Meaning and How to Calculate It

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Year-over-year (YoY) is a way of measuring change by comparing a figure for one period with the same period one year earlier. Examples include this quarter’s revenue against the same quarter last year, or this March’s sales against last March’s. The result is usually stated as a percentage. “YoY” is the acronym, and “year-on-year” means the same thing.

What Is Year-Over-Year (YoY)?

YoY answers a simple question: is this number higher or lower than it was at the same point last year, and by how much? It shows whether performance is improving, flat or worsening.

In finance, YoY appears in earnings releases (“revenue rose 8% year over year”), analyst reports and economic statistics. It applies to any metric tracked over time, such as units sold, active customers, store traffic or costs.

How Year-Over-Year Works

Calculating Year-Over-Year

The standard YoY growth formula is:

YoY growth (%) = (Current period value ÷ Same period last year − 1) × 100

An equivalent form is (Current − Prior) ÷ Prior × 100. The prior-year figure is always the denominator, because growth is measured relative to where the number started.

The two periods must match exactly. Compare Q2 with the previous Q2, or July with the previous July. To track YoY monthly, repeat the calculation each month against the same month a year earlier, producing a rolling series of twelve-month changes.

Interpreting Year-Over-Year

A positive result means growth; a negative result is a YoY decline. A sequence of YoY figures tells you more than any single one: growth that moves from 12% to 9% to 5% means the metric is still rising, but more slowly each period.

When the metric is already a percentage, keep two kinds of change separate:

• Percentage-point change. An operating margin that rises from 20% to 22% has increased by 2 percentage points.
• Percent change. That same move is a 10% increase in the margin itself.

Why Is Year-Over-Year Important?

Most businesses have peak and slow seasons. Retailers typically do much of their selling in the fourth-quarter holiday period. Comparing a retailer’s Q4 with its Q3 could suggest dramatic growth that is really just the season. Comparing Q4 with the following Q1 could suggest a collapse for the same reason. Setting Q4 against the prior Q4 removes that distortion and isolates the actual change in the business.

YoY figures also make data easier to compare across time and across companies. An investor can line up several years of first-quarter revenue and see at a glance whether the trend is up or down, and can apply YoY to a portfolio’s returns in the same way.

On the economic side, headline inflation is usually reported as the YoY change in the Consumer Price Index; see U.S. inflation rate by year.

Example of Year-Over-Year

Hypothetical example. A company reports Q3 revenue of $540 million. Its Q3 revenue a year earlier was $480 million.

($540M ÷ $480M − 1) × 100 = 12.5% YoY revenue growth

Now suppose its earnings fall from $60 million to $54 million over the same periods:

($54M ÷ $60M − 1) × 100 = −10% YoY

The two results tell different stories. Sales grew, but profit shrank, so costs rose faster than revenue. Analysts often run the same calculation on earnings per share, which also reflects changes in the share count.

Limitations of Year-Over-Year

• Base effects. An unusually weak prior year inflates the current growth rate, and an unusually strong one suppresses it. A 40% rebound after a 30% drop still leaves the metric below where it started.
• Only two points. A single YoY figure says nothing about what happened in between. It can hide a business that peaked mid-year and is now declining.
• Calendar quirks. Leap years, 53-week fiscal years and holidays that shift between months (such as Easter) can make “the same period” slightly different.
• Structural changes. Acquisitions, divestitures, accounting changes and currency moves can produce YoY growth that has nothing to do with the underlying business. This is why companies sometimes also report “organic” or “constant-currency” growth.
• Nominal vs. real. A 5% YoY rise in sales during a year of 4% inflation is much less than it appears. Adjusting for inflation gives the real change.
• Negative or zero bases. If last year’s figure was a loss or zero, the percentage is meaningless or undefined. Report the dollar change instead.

YoY vs. Related Measures

YoY vs. YTD. Year-to-date (YTD) measures change, or accumulates a total, from the start of the current calendar or fiscal year up to today. YTD is a running total, while YoY compares two comparable periods twelve months apart.

YoY vs. sequential. Sequential comparisons set a period against the one immediately before it: quarter-over-quarter (QoQ) or month-over-month (MoM), such as phones sold in Q4 versus Q3, or airline seats filled in January versus December. They react faster to turning points but carry seasonal noise. The same formula applies to any time frame.

YoY vs. CAGR. Compound annual growth rate smooths growth over several years into one average annual rate. YoY measures only a single year’s change.

Trailing twelve months (TTM). TTM sums the latest four quarters. Comparing one TTM total with the prior TTM total is a YoY comparison of full-year figures. Ratios such as the P/E ratio often use TTM earnings.

FAQs

The Bottom Line

YoY figures matter to investors reading earnings releases, analyst reports and inflation data. A single YoY number gives a useful snapshot, yet it can mislead when the prior year was unusually weak or strong, or when acquisitions, currency moves or inflation drive the change. Reading a sequence of YoY figures alongside sequential, CAGR or organic growth measures gives a fuller picture of how a business is really performing.