A year-over-year calculation compares a statistic for one period to the same period the previous year. The period is for a month or quarter basis. The year-over-year growth rate calculates the percentage change during the past twelve months.
Year-over-year (YOY) is an effective way of looking at growth for two reasons. First, it removes the effects of seasons. For example, say your business revenue rose 20% last month. Before you break out the bubbly, check it against the income from the same month last year. Maybe your sales always rise this time of year. If sales typically rise 35% this month, then your revenue is down year-over-year. Your business is doing worse, not better.
Second, it discerns long-term trends. Say a business is growing at a nice, steady 2% a month. But if it grew 3% a month last year, it will be down when compared year-over-year.
For these reasons, make sure you check what comparisons a financial report is using. Are the authors comparing the data to the previous full year, such as 12 months of accumulated revenue, or to a statistic's value as of the last period of the quarter, month, week, or day? Also, check to see if they are using the calendar year or fiscal year.
If you're thinking about using the YOY statistic, the following snapshot of the pros and cons can help you apply the metric more effectively.
- Year-over-year is a calculation that helps compare growth over the previous 12 months.
- YOY is a great statistic to use when you want to control the effects of volatility when comparing companies or economies.
- While a helpful statistic, it does a poor job of capturing the full picture because it leaves important information out.
- This statistic can be used to reveal trends that signal an economic downturn.
Negates seasonality because it compares specific points in time.
Smoothes out volatility throughout the year to compare net results.
Easy to calculate; no need for spreadsheet or financial calculator.
States results in percentage terms for an easy comparison across different-sized companies.
Offers meaningless results if one time period had negative growth.
Can hide problems in a given month if only comparing full-year metrics YOY.
Doesn't offer much information unless used with other metrics.
Pros and Cons
The biggest advantage of year-over-year comparisons is that they automatically negate the effect of seasonality. For example, retail statistics rise each November and December because of the holiday shopping season. It's the most critical time of the year as the season accounts for almost 20% of retail sales. Another advantage is that the metric is stated in percentage terms, making it easy to compare different-sized companies when doing industry, competitor or peer-company analysis.
Year-over-year analysis helps smooth out any volatility in the month-to-month numbers. For example, the Bureau of Labor Statistics reported that the economy only added 18,000 jobs. in June 2011. Investors should have used a year-over-year comparison. They panicked because it was less than the February through April monthly average of 215,000 jobs. The stock market dropped. The prices of safe haven investments like Treasuries and gold sky-rocketed. Thanks to that panic, gold hit an all-time high of $1,917.90 an ounce a few months later in August 2011.
In this case, the calculation seemed misleading when using individual months YOY, but when using full-year results, the calculation showed that the total number of employed people had increased by 1.425 million between June 2010 and June 2011. The economy’s recovery had not derailed. There are more examples like these in the current jobs report and the current unemployment report.
Don’t rely on year-over-year alone. It's a good idea to look at month-to-month as well to get the full picture.
A few issues can arise with the YOY calculation, especially if a company experiences a period of negative growth. The resulting growth rate won't make sense. Also, as with many other business metrics, the YOY statistic provides much more information when calculated for a few time periods to reveal trends, and doesn't really explain enough of a company's growth story unless used along with other metrics.
If you rely only on the YOY metric, calculated with full-year values, you may also miss problems such as abnormally low growth in one month, which gets smoothed out if using a full-year number for the calculation.
Most business news reports monthly trends. You usually have to seek out the year-over-year number yourself, but you can find the formula inputs on a company's financial statements and easily calculate the statistic with a standard calculator.
How to Calculate the Year-Over-Year Growth Rate
To calculate the year-over-year growth rate, you need two numbers and a calculator. Then take these three steps.
- Subtract last year's number from this year's number. That gives you the total difference for the year. If it's positive, it indicates a year-over-year gain, not a loss. For example, this year you sold 115 paintings. Last year you sold 110. You sold 5 more paintings this year.
- Then, divide the difference by last year's number. That's 5 paintings divided by 110 paintings. That gives you the year-over-year growth rate.
- Now simply put it into percent format. You find 5 / 110 = 0.045 or 4.5%.
Let’s return to the employment example. In June 2011, total employment was 131.955 million. Total employment in June 2010 was 130.530 million. Here's how to calculate the year-over-year growth rate.
- Subtract 130.530 million from 131.955 million. The difference is 1.425 million.
- Divide 1.425 million by 130.530 million, last year's employment number.
- The answer is 0.0109 or 1.09%. That's the year-over-year growth rate.
Most government statistics are month-to-month or quarter-to-quarter. You'll need to calculate the year-over-year numbers yourself to get the full picture. Here are three leading economic indicators where it's important to do year-over-year calculations:
- Durable Goods: The Commerce Department reports this statistic month-to-month. But YOY calculations warned of the Great Recession as early as October 2006.
- Manufacturing Jobs: America had been losing manufacturing jobs on a monthly basis for years. But when jobs started declining YOY in 2007, it was a sign of the pending recession.
- Gross Domestic Product: It says how fast the economy grew in the most recent quarter. The Bureau of Economic Analysis annualizes the GDP growth rate. It reports how much the economy would produce for the entire year if it continued growing at the same rate. The BEA does that so it’s easier for you to do a YOY comparison with previous years of GDP growth.