Year-over-year growth: the formula, the meaning, and a calculator.
Year-over-year (YoY) growth compares a number this period to the same period one year ago. It smooths out seasonality so you can see the real trend. Here is the formula, three worked examples, and a calculator that does the math for you.
Year-over-year growth is one of the most useful numbers your books can give you. It tells you whether revenue is rising, expenses are creeping up, or sales are picking up over time. Comparing one month to the next gets noisy. Comparing this January to last January does not.
YoY gives you an annualized view of performance that strips out seasonal swings and one-time spikes.
It works for any metric you have at least 12 months of data on: revenue, profit, customers, page views, daily sales.
What year-over-year growth is
What does YoY mean?
YoY stands for year-over-year. It compares a number from one period to the same period a year earlier (this January to last January, this Q1 to last Q1), so seasonal swings do not distort the trend. YoY growth is the percentage change between the two: ((current − prior) ÷ prior) × 100.
Year-over-year growth, often called YoY or annualizing, compares a number from a current period (this month, quarter, or year) to the exact same period one year earlier. Because the two windows match, the result shows real change rather than the noise of a holiday week or a slow February.
It is different from month-over-month growth, which compares this month to last month, and quarter-over-quarter growth, which compares this quarter to last quarter. YoY is the one you reach for when seasonality is in the way.
Businesses calculate YoY for almost anything: revenue, profit, customers acquired, website traffic. The only requirement is having data that goes back at least 12 months so the comparison is true apples to apples.
The formula
To calculate the year-over-year growth of any number, do three things:
- Subtract last year's value from this year's value.
- Divide the result by last year's value.
- Multiply by 100 to get the percentage.
In a spreadsheet, that is one line. If this January is $50,000 and last January is $40,000, your YoY growth is 25 percent.
=(Current - LastYear) / LastYear * 100
The calculator
Plug in the two numbers and the calculator does the math. Click a sample to load the worked examples from this article.
Example one: revenue growth
Say your company wants its year-over-year revenue growth for January. The business earned $50,000 this January and $40,000 in the same month last year.
(50,000 − 40,000) ÷ 40,000 × 10010,000 ÷ 40,000 × 1000.25 × 100Monthly revenue grew 25 percent year over year. A clean win.
Example two: website traffic
The formula works the same for non-financial numbers. Same equation, different inputs.
Say your site pulled 30,000 page views in Q1 this year, against 25,000 in the same quarter last year.
(30,000 − 25,000) ÷ 25,000 × 1005,000 ÷ 25,000 × 1000.20 × 100Quarterly traffic grew 20 percent year over year.
Example three: daily net income
Now a daily comparison. Imagine you run a restaurant and Canada Day is your biggest day of the year. In year one of business, that day was so far above every other day that you had nothing to compare it to. A year later, you do.
Net income this Canada Day was $1,756. Same day last year was $1,288.
(1,756 − 1,288) ÷ 1,288 × 100468 ÷ 1,288 × 1000.3634 × 100The day grew 36.3 percent year over year. Worth celebrating.
Why YoY matters for a small business
It accounts for seasonality. Many businesses run hot in one season and quiet in another. A retailer's Q4 is a different animal from its Q2. Comparing Q4 to Q2 makes the year look better than it is. Comparing this Q4 to last Q4 takes seasonality out of the picture and shows whether the business is actually growing.
It gives you a long-term read. Daily and weekly numbers tell you what is happening right now. YoY tells you whether the long arc of the business is bending up or down. Both are useful, but only one of them survives a bad week.
How do you calculate year-over-year growth?
Subtract last year's value from this year's value, divide by last year's value, and multiply by 100. The formula is ((current − prior) ÷ prior) × 100. Example: $50,000 this January and $40,000 last January is 25 percent growth. Always compare matching periods: January to January, Q1 to Q1, Canada Day to Canada Day.
Where Numinor fits
A reliable YoY number starts with reliable books. If transactions are mis-categorized or accounts are not reconciled, the comparison is built on sand. Numinor handles bookkeeping for small businesses across Canada: monthly reconciliation, consistent categorization, and financial statements you can trust when you sit down to compare two periods.
If you would like a second set of eyes on your books before you start running comparisons, we offer a free books review. Honest read, no obligation.
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