YoY explained: how to calculate and analyse year-over-year change

Year-over-year compares the same period in different years

Year-over-year (YoY) is a common way of measuring change in economic and company data. Traders may see it alongside figures such as inflation, GDP, revenue and earnings, where it helps show how the latest result compares with a year earlier.

YoY compares a figure for the current period with the same period one year earlier. For example, monthly inflation may be compared with the same month last year, while a company’s quarterly revenue may be compared with the same quarter last year.

This type of comparison can help show how a figure has changed over a 12-month period while reducing the effect of seasonal differences between months or quarters. A positive YoY change means the figure has increased from a year earlier, while a negative change means it has decreased.

YoY differs from month-over-month (MoM) or quarter-over-quarter (QoQ) comparisons, which measure changes from the immediately preceding period. These shorter-term comparisons provide a more recent view of changes, while YoY provides a longer-term comparison with the same period in the previous year.

How to calculate YoY change

YoY change shows how much a figure has increased or decreased compared with the same period one year earlier. It is usually expressed as a percentage, making it easier to compare changes across different periods, companies or economic indicators.

The YoY formula

To calculate YoY change, subtract the previous year's value from the current value, divide the difference by the previous year's value and multiply by 100:

YoY change = ((current value − previous year's value) ÷ previous year's value) × 100

The calculation has three steps:

• Find the difference: subtract the previous year's value from the current value.
• Compare it with the previous value: divide that difference by the previous year's value.
• Convert it to a percentage: multiply the result by 100.

A positive result means the figure has increased from a year earlier, while a negative result means it has decreased.

Example: revenue increases from $12m to $15m

Suppose a company reports revenue of $15 million in Q2 2026, compared with $12 million in Q2 2025.

Using the YoY formula:

(($15m − $12m) ÷ $12m) × 100 = 25%

The company's revenue therefore increased by 25% YoY compared with Q2 2025.

How to read YoY percentages

A positive YoY percentage indicates an increase from the same period a year earlier, while a negative percentage indicates a decrease. For example, 10% YoY means the figure is 10% higher than a year earlier, while -10% YoY means it is 10% lower.

However, the percentage should also be considered alongside the underlying figures. A large percentage increase from a low starting point can represent a relatively small change in absolute terms. Looking at both the percentage and the underlying values gives you a clearer picture of the scale of the change.

Why YoY is useful for seasonal data

Some economic and company data follows predictable seasonal patterns. Retail sales may rise during the holiday period, for example, while activity in other industries can vary depending on the time of year. Comparing consecutive months or quarters can therefore reflect normal seasonal changes rather than a meaningful shift in performance.

YoY comparisons can help reduce this effect by comparing equivalent periods. If a retailer typically records stronger sales in Q4 than Q3, comparing Q4 with the same quarter a year earlier can provide a more useful indication of how its performance has changed.

This does not remove the effects of seasonality completely, but it can make underlying changes easier to identify. This is one reason YoY figures are commonly used for economic indicators and company data such as inflation, retail sales, GDP, employment, revenue and earnings.

Where traders see YoY figures

YoY figures appear frequently in company reports and economic data releases. They can help traders assess how company performance, prices and economic activity have changed compared with a year earlier.

Common examples include:

• Company earnings: revenue, profit, earnings per share (EPS) and other performance measures may be reported on a YoY basis.
• Inflation: indicators such as the Consumer Price Index (CPI) often show how prices have changed over the previous 12 months.
• Economic growth: GDP can be reported as a YoY change to show how economic output compares with a year earlier.
• Retail sales and employment: YoY figures can provide a longer-term view of changes in consumer spending and labour market conditions.
• Industry and sector data: YoY comparisons can show how demand, sales or activity have changed across particular sectors or regions.

These figures may appear in earnings releases, economic calendars, company presentations, market news and research. Knowing what the YoY percentage refers to is the first step, but it is also important to consider whether YoY is an appropriate comparison for that particular metric.

Which metrics are most useful for YoY comparisons?

YoY comparisons are particularly useful for figures measured over a period of time, such as a month or quarter. Revenue, earnings, retail sales and GDP are examples because they measure activity during a defined period that can be compared with the equivalent period a year earlier.

YoY can also be useful for metrics affected by seasonal patterns. For example, retailers may compare same-store sales with the same period a year earlier, while airlines may compare passenger numbers or capacity with the equivalent period in the previous year.

Point-in-time figures, such as cash, debt or inventory on a particular date, require more context. A YoY comparison can still show how these figures have changed from a year earlier, but the percentage alone may not explain why they changed or what that means for the business.

When interpreting these figures, consider the underlying values and relevant company or economic context alongside the YoY percentage.

How expectations affect market reactions to YoY data

A positive YoY figure does not necessarily lead to a positive market reaction. Traders also consider how the result compares with expectations, previous readings and other information in the release.

For example, a company could report revenue growth of 20% YoY but fall short of a 25% consensus forecast. Despite strong growth compared with the previous year, the weaker-than-expected result could put pressure on its share price. Conversely, growth of 8% could be received positively if analysts had expected 5%.

The same principle applies to economic releases. If YoY inflation is higher than expected, traders may reassess expectations for interest rates, potentially affecting currencies, bonds and stock indices. Weaker-than-expected GDP, retail sales or employment data can also change expectations for the economic outlook.

This is why traders should avoid interpreting YoY figures as simply ‘good’ or ‘bad’. The result needs to be considered alongside forecasts, previous readings and the wider context of the release.

YoY compared with shorter-term measures

YoY is one of several ways to compare performance over time. While YoY compares a figure with the same period one year earlier, quarter-over-quarter (QoQ) and month-over-month (MoM) focus on more recent changes. Year-to-date (YTD) shows performance from the beginning of the year to the current point.

Looking at these comparisons together can provide a more complete picture of both recent changes and longer-term trends.

Quarter-over-quarter compares consecutive quarters

Quarter-over-quarter (QoQ) compares the latest quarter with the quarter immediately before it. This can help traders identify changes in company performance or economic activity that may not yet be as visible in YoY figures.

For example, a company's revenue could increase from Q1 to Q2 while remaining lower than Q2 the previous year. In this case, QoQ would show recent improvement while YoY would still show a decline.

Seasonality can affect QoQ comparisons because consecutive quarters may naturally have different levels of activity. This is why QoQ and YoY can provide different, but complementary, views of the same data.

Month-over-month shows more recent changes

Month-over-month (MoM) compares a figure with the previous month. It is commonly used for economic indicators such as inflation and retail sales, where traders may want to see how conditions are changing over shorter periods.

Because MoM covers a shorter time frame, it can be more affected by temporary events, seasonal patterns or other short-term changes. A single strong or weak month therefore does not necessarily indicate a longer-term trend.

Looking at MoM alongside YoY can help distinguish recent changes from the broader 12-month picture.

Year-to-date tracks performance within the current year

Year-to-date (YTD) refers to the period from the beginning of the current calendar or fiscal year to the latest available date. It can be used to track cumulative figures such as revenue or investment performance during the year.

YTD differs from YoY because it does not automatically compare the current figure with the previous year. For example, revenue reported YTD in September represents total revenue from the beginning of the year through September.

To assess how that performance has changed from a year earlier, the current YTD figure can be compared with the equivalent YTD period in the previous year.

Base effects and other limitations of YoY

YoY comparisons can sometimes make changes appear larger or smaller than the underlying trend. One common reason is the base effect, where an unusually high or low figure from the previous year affects the percentage change.

For example, if revenue was unusually low during the same quarter last year, a return to more typical levels could produce a large positive YoY percentage. Conversely, an unusually strong previous year can make current performance appear weak even if the latest figure remains relatively high.

One-off events can also affect YoY comparisons. Store closures, supply disruptions, acquisitions, tax changes or other unusual events may influence either period, making a direct comparison less representative of normal conditions.

When interpreting YoY data, consider:

• The underlying values: a large percentage change from a small starting value may represent a relatively small change in absolute terms.
• One-off events: unusual circumstances affecting either period can distort the comparison.
• Inflation: an increase in nominal revenue or spending does not necessarily represent the same increase in real terms once changes in prices are considered.
• Data revisions: economic figures can be revised after their initial release, changing the YoY comparison.
• Recent changes: MoM and QoQ figures can provide additional context about developments that may not yet be clear in YoY data.

YoY is therefore most useful when the percentage is considered alongside the figures behind it and the circumstances affecting both periods.

How traders can interpret YoY data

YoY figures can provide useful context, but they should not be treated as standalone trading signals. Their significance depends on what is being measured, how the figure compares with expectations and what other data shows.

When reviewing a YoY figure, traders can consider the underlying value first. This can help show whether a large percentage represents a substantial change or is partly the result of a low or high comparison base.

Shorter-term data can provide another perspective. MoM and QoQ figures may show whether a recent change is strengthening, slowing or moving in a different direction from the YoY trend.

For company results, other measures such as margins, cash flow and earnings can help provide a broader view of performance. Comparing results with previous periods, forecasts and relevant industry data can also help put the YoY figure into context. For economic releases, related indicators can help show whether the change reflects a broader economic trend.

Taken together, these comparisons can help traders understand what has changed, over what time frame and whether the latest YoY figure adds meaningful new information.