Understanding Year-over-Year (YoY) Percentage Change
Year-over-year (YoY) percentage change compares a metric now to the same point twelve months ago — this quarter's revenue against last year's same quarter, this month's traffic against the same month last year. It uses the same formula as any percentage change calculation, applied specifically to a twelve-month comparison window.
Already have your two numbers?
YoY uses the exact same math as the site's main calculator — enter last year's figure as the old value and this year's as the new value.
The formula
YoY Change % = ((Current − Prior) ÷ Prior) × 100
An algebraically identical alternative appears just as often in finance content: (Current ÷ Prior − 1) × 100. Both return the same number.
Worked example
A company's Q4 revenue was $80,000 last year and $100,000 this year:
YoY Change % = ((100,000 − 80,000) ÷ 80,000) × 100 = 25%
The rule that actually trips people up
The math is simple. What causes real errors is comparing periods that don't actually match. The U.S. Bureau of Labor Statistics is explicit about this in its own methodology for calculating percent changes in the Consumer Price Index: the beginning and ending periods "must always be the same month," and a calculation using January and December data produces an eleven-month change, not a year-over-year one.
This isn't a theoretical concern. It shows up constantly in real spreadsheet and dashboard work. In one Microsoft Fabric community thread, a user built a year-over-year measure in Power BI and got 20.2% back when the correct answer for their numbers (9,242 versus 8,558) was 7.99% — independently recalculated here and confirmed correct. The cause, per the thread's replies, was a filter-context bug pulling in the wrong comparison period, not a formula typo. Several similar threads on Qlik's community forum show the same underlying pattern: people know the concept but the implementation quietly grabs the wrong "prior period."
Is 15–20% YoY growth good?
There's no single right answer — it depends heavily on company stage and industry. Wall Street Prep's own guidance notes that late-stage, mature companies with established market share are unlikely to sustain the same growth rates as early-stage companies, and that a slowing growth rate isn't automatically a bad sign if the underlying revenue quality has improved.
Sources that publish a specific benchmark range don't fully agree with each other: LivePlan cites 15–25% as healthy small-business growth, while other guidance puts the range closer to 10–20% or 10–25% depending on industry. Treat any single number here as a loose reference point, not a target — the spread between these figures is itself a sign that industry and company stage matter more than the exact percentage.
YoY vs. MoM, QoQ, and YTD
These are all percentage-change calculations applied to different windows, and mixing them up changes what the number actually means.
| Metric | Compares | Best for |
|---|---|---|
| Month-over-Month (MoM) | This month vs. last month | Short-term tracking, but sensitive to seasonal swings |
| Quarter-over-Quarter (QoQ) | This quarter vs. last quarter | Medium-term trend, less noisy than MoM |
| Year-over-Year (YoY) | This period vs. the same period last year | Removes seasonal distortion entirely |
| Year-to-Date (YTD) | Start of this year vs. now | Cumulative progress within the current year |
A seasonal business is the clearest case for why this matters: a restaurant's revenue might spike every summer from tourism. Looking only at MoM growth from June to August would show what looks like explosive growth; looking at YoY for the same months removes that seasonal noise and shows the real underlying trend.
See the related breakdown: percentage change vs. percentage difference vs. percentage points →
Frequently asked questions
Is 15% YoY growth good?
It depends on company stage and industry — there's no universal answer, and even published benchmarks don't fully agree. LivePlan cites 15–25% as healthy small-business growth; other sources put it closer to 10–20%. Mature companies should expect lower rates than that, and that's not a bad sign on its own.
Is 1% per month the same as 12% per year?
No. Compounded monthly, 1% growth becomes 12.68% annually, not 12% — each month's growth applies to an already-larger base, not the original starting value.
What's an example of a year-over-year comparison?
Comparing this December's sales to last December's sales, or this quarter's website traffic to the same quarter last year.
How is YoY different from month-over-month?
MoM compares consecutive months and is sensitive to seasonal swings. YoY compares the same month across two years, which removes that seasonal noise.
Why did my spreadsheet give me the wrong YoY percentage?
The most common cause found in real user reports is comparing mismatched periods — the tool pulling last month instead of the same month last year, often from a filter or reference-cell error, not the formula itself.
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Cedrick Reese, Founder
I'm Cedrick Reese, a retired veteran and web developer who built PercentageChangeCalculators.com as part of Ready Utilities, my collection of free, user-friendly online tools. My journey began in the early 2000s with affiliate marketing and niche site development, which grew into a passion for creating practical digital utilities and calculators. After retiring, I earned a Computer Systems Technician certificate from UEI College, completed Electro-Mechanical Technologies at Tulsa Welding School, and finished the Carpentry program at Florida State College at Jacksonville. Today, I combine my technical background and craftsmanship by building furniture using traditional woodworking methods, gardening, and developing helpful online tools for users worldwide.