Calculate Year-Over-Year Percentage Change

Calculate year-over-year (YoY) percentage change by subtracting the value from the same period last year from the current value, dividing by last year’s value, and multiplying by 100. Enter those two values to get the percentage increase or decrease, along with the absolute difference.

Formula

YoY percentage change = [(current value − previous-year value) ÷ previous-year value] × 100.

• Current value is the measured amount for the period being assessed. It may be a count, revenue total, price, quantity, or another numerical measure.
• Previous-year value is the corresponding measure for the same period one year earlier.
• YoY percentage change is the relative difference, expressed as a percentage. A positive result indicates an increase; a negative result indicates a decrease.

The two values should use the same unit and cover comparable periods. The result is a percentage, so it does not inherit the units of the input values. The absolute difference, shown as a helper, keeps the original unit.

Worked Example

Using the calculator’s defaults, the current value is 120 and the value for the same period last year is 100.

1. Subtract the previous-year value: 120 − 100 = 20.
2. Divide by the previous-year value: 20 ÷ 100 = 0.2.
3. Multiply by 100 to express the ratio as a percentage: 0.2 × 100 = 20.00%.

The value increased by 20.00% year over year, an absolute increase of 20 units. If the current value were 80 instead, the calculation would be (80 − 100) ÷ 100 × 100 = −20%, a 20% decrease.

When to Use Year-Over-Year Change

YoY comparisons are useful when a measure follows a repeating annual pattern. Comparing a given month or quarter with the same month or quarter a year earlier can help reduce the effect of seasonality—for example, comparing December sales with the previous December rather than with November.

The method applies broadly, provided the measure and periods are defined consistently. Examples include comparing a company’s quarterly revenue, a school’s annual enrollment, monthly website visits, or the number of items produced in a particular month. It describes the change between two observations; by itself, it does not explain why the change happened.

Use matching intervals: month to same month, quarter to same quarter, or year to year. If a reporting period uses a fiscal calendar, compare the equivalent fiscal period rather than assuming it matches a calendar month or quarter.

How to Interpret the Result

A positive result means the current value is higher than the comparison value. A negative result means it is lower. A result of 0% means both values are equal, assuming the comparison value is nonzero. Read the sign and magnitude together: −8% indicates a decline, while +8% indicates growth.

Percentages express relative change, not the size of the underlying difference. An increase from 10 to 20 is 100%, while an increase from 1,000 to 1,010 is 1%, even though the second change is larger in absolute units. For that reason, it is often useful to report both the percentage change and the numerical difference.

Rounding can affect the displayed result. Calculate with the original values, then round the final percentage to a suitable number of decimal places. The calculator displays two decimal places; this is a presentation choice, not a claim that the source data are precise to that level.

Common Problems and Limitations

• Zero as the previous value: division by zero is undefined, so a standard YoY percentage change cannot be calculated when last year’s value is zero. Report the two values and their absolute difference, or describe the change without assigning a percentage.
• Very small comparison values: a small denominator can produce a very large percentage. Check the underlying amounts before interpreting the percentage as meaningful or important.
• Unmatched periods: comparing a full quarter with only part of a quarter, or one month with a different month, can mislead. Align the duration and scope of both observations.
• Changed definitions or units: make sure both figures measure the same thing. If one value is recorded in dollars and the other in thousands of dollars, convert them to a common scale first.
• Revised or incomplete data: source figures may be corrected later, and a current period may not yet be complete. Note whether values are final and whether the periods cover equal amounts of time.

YoY change is a descriptive comparison, not a forecast or a measure of cause and effect. It does not adjust for inflation, population growth, changes in accounting or measurement methods, or other factors unless those adjustments are made to the inputs first. A rate of change can also look different from a percentage-point difference: for instance, a movement from 10% to 12% is a rise of 2 percentage points, but a 20% relative increase from the original 10%.

Frequently Asked Questions

How do I calculate YoY percentage change in Excel?
Put the current value in one cell and the same-period-last-year value in another. If the current value is in B2 and the earlier value is in A2, use =(B2-A2)/A2 and format the result as a percentage. Do not multiply by 100 as well if the cell is already percentage-formatted.

Can YoY percentage change be negative?
Yes. A negative result means the current value is below the previous-year value. For example, a result of −12% indicates a 12% decrease relative to the previous-year figure.

What if last year’s value was zero?
The formula requires division by the previous-year value, so it is undefined when that value is zero. State the current and previous values and, where useful, give their absolute difference instead of presenting a percentage.

Is YoY change the same as year-over-year growth?
They commonly refer to the same calculation. “Growth” is often used when the result is positive, while “change” can describe increases, decreases, or no change.

What is the difference between YoY and month-over-month change?
YoY compares a period with the corresponding period a year earlier. Month-over-month compares it with the immediately preceding month. The latter can show more recent movement but may be more affected by seasonal patterns.

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in current | Current period value | - | 120 | 0
in previous | Same period last year | - | 100 | 0
out change | YoY percentage change | % | (current - previous) / previous * 100 | 2
out difference | Absolute change | - | current - previous | 2