YoY Change Formula: How to Calculate Year-Over-Year Growth

The year-over-year (YoY) change formula calculates the percentage difference between a value in one period and the same period in the previous year. To compute it, subtract last year’s value from this year’s value, divide the result by last year’s value, and multiply by 100. For example, if revenue was $120,000 this year and $100,000 last year, the YoY change is (120,000 – 100,000) / 100,000 × 100 = 20%.

Formula

The standard YoY change formula is:

YoY Change (%) = [(Current Period Value – Previous Year Value) / Previous Year Value] × 100

Where:

• Current Period Value – the metric from the most recent period (e.g., Q3 2025 revenue, December 2025 sales, 2025 total users).
• Previous Year Value – the same metric from the same period one year earlier (e.g., Q3 2024 revenue, December 2024 sales, 2024 total users).

The result is expressed as a percentage. A positive result indicates growth; a negative result indicates a decline. If the previous year value is zero, the formula is undefined because division by zero is not possible.

Worked Example

Using the default values from the calculator above:

1. Current year value = $120,000
2. Previous year value = $100,000
3. Difference = $120,000 – $100,000 = $20,000
4. Divide by previous year: $20,000 / $100,000 = 0.20
5. Multiply by 100: 0.20 × 100 = 20%

The YoY change is 20%. This matches the calculator output (rounded to two decimal places).

Why Use YoY Instead of Month-over-Month or Quarter-over-Quarter?

YoY comparisons are widely used because they eliminate seasonal effects. Retail sales, for example, spike in December and drop in January; comparing December 2025 to December 2024 gives a fairer picture of underlying growth than comparing December 2025 to November 2025. Similarly, comparing Q4 2025 to Q4 2024 accounts for holiday seasonality that a quarter-over-quarter comparison would not. YoY is also less volatile than shorter-period comparisons because it smooths out one-off events like a single bad month or a temporary supply disruption. However, YoY can mask recent trends – if a company had a strong Q1 but a weak Q3, the YoY figure for Q3 might still look positive because Q3 of the prior year was even weaker. For that reason, many analysts look at both YoY and sequential (quarter-over-quarter) changes.

How to Read the Result

A YoY change of 20% means the current value is 20% larger than the value from the same period last year. A YoY change of –15% means the current value is 15% smaller. The percentage is relative to the previous year, not to the current year. For example, if revenue went from $100 to $120, that is a 20% increase. If it then drops from $120 to $100, the YoY change is –16.7%, not –20%, because the drop is calculated relative to $120. This asymmetry is a common source of confusion. Always note the base year when interpreting a YoY figure.

Common Mistakes and Pitfalls

• Using different time periods – The current period and the previous year period must cover the same length of time (e.g., full year vs. full year, or Q1 vs. Q1). Comparing a single month to a full year will give a meaningless result.
• Forgetting to multiply by 100 – The formula yields a decimal (0.20) unless you multiply by 100 to get a percentage (20%).
• Dividing by the current year instead of the previous year – The denominator is always the previous year’s value. Dividing by the current year gives a different number (e.g., 120/100 = 1.2 vs. 100/120 = 0.833).
• Ignoring negative values – If the previous year had a loss (e.g., –$10,000) and the current year has a profit ($5,000), the formula produces a negative percentage that is hard to interpret. In such cases, it is often better to report the absolute change or use a different metric.
• Rounding too early – Round only the final percentage, not intermediate steps, to avoid small errors that can compound.

When YoY Change Is Not Appropriate

YoY change works best for metrics that are roughly stable in scale and have a meaningful previous-year baseline. It is less useful when:

• The previous year value is zero or near zero, making the percentage enormous or undefined.
• The metric is new and has no prior-year data.
• The business or economy has undergone structural changes (e.g., a merger, a new product line, or a regulatory shift) that make the prior year not comparable.
• You need to detect a sudden change within the year – a month-over-month or quarter-over-quarter comparison would be more responsive.

In these situations, consider using absolute changes, index numbers, or moving averages instead.

Alternatives to YoY Change

Several other metrics complement or replace YoY change:

• Month-over-month (MoM) or quarter-over-quarter (QoQ) change – compares to the immediately preceding period; more sensitive but noisier.
• Compound annual growth rate (CAGR) – smooths growth over multiple years into a single annualized rate. Formula: [(Ending Value / Beginning Value)^(1 / Number of Years)] – 1.
• Year-to-date (YTD) change – compares the current partial year to the same period last year (e.g., Jan–Sep 2025 vs. Jan–Sep 2024). This is a form of YoY but for a partial year.
• Absolute change – simply the difference in units (e.g., $20,000), which is sometimes more meaningful when the percentage is misleading due to a small base.

Each metric answers a different question. YoY tells you how the current period compares to the same period last year; MoM tells you how it compares to the previous month; CAGR tells you the average annual growth over a multi-year span.

Frequently Asked Questions

What is the difference between YoY and YTD?

YoY compares a complete period (e.g., full year, Q3) to the same period one year earlier. YTD compares the start of the current year up to a specific date (e.g., January 1 to September 30) to the same date range in the previous year. YTD is a partial-year YoY comparison.

Can YoY change be negative?

Yes. If the current period value is lower than the previous year value, the result is negative, indicating a decline. For example, if revenue fell from $100,000 to $90,000, the YoY change is –10%.

What if the previous year value is zero?

The formula is undefined because you cannot divide by zero. In that case, report the absolute change or simply state that the metric grew from zero to the current value, but avoid quoting a percentage.

How do I calculate YoY growth in Excel or Google Sheets?

If cell A1 holds the current year value and B1 holds the previous year value, enter =(A1-B1)/B1 and format the cell as a percentage. This gives the YoY change directly.

Is YoY the same as annual growth rate?

Not necessarily. YoY compares a specific period to the same period last year. Annual growth rate often refers to the full-year change, but it can also be annualized from a shorter period. For a full-year comparison, YoY and annual growth rate are the same.

Why do companies report YoY instead of just the current number?

YoY provides context. A single number like “$120,000 in revenue� is hard to evaluate without a baseline. YoY tells you whether that number is better or worse than the same time last year, which helps investors and managers assess performance.

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in cur | Current year value | $ | 120000 | 0
in prev | Previous year value | $ | 100000 | 0
out yoy | YoY change | % | ((cur - prev) / prev) * 100 | 2