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Year-over-year (YoY)

Year-over-year (YoY) is a comparison of a period with the same period a year earlier, so that seasonality does not pass for growth or decline.

How it works

A month-over-month comparison mixes seasonality into the result: a gift shop’s December beats November mostly because of the holidays. Compared with last December, the season sits on both sides and drops out. What remains is the store’s own change plus whatever moved in the market. To compare at all, a store needs a full year of history before the window.

Two things still leak in. The calendar: the same dates fall on different weekdays, and holidays move. And the budget: revenue rises with spend, so read revenue, spend and ROAS side by side. The guide to year-over-year growth shows how to tell demand from budget.

Formula

(This period − same period last year) ÷ same period last year × 100%

Where you see it

  • GetProfit portal: Assortment and seasonality compares a 90-day window with the same 90 days a year earlier, by product type, category or brand. Without enough history for last year’s window, the portal draws no chart and says there is nothing to compare with.

Example

Example store, not client data.

The tableware shop took 288,000 in November against 180,000 in October: +60% month over month, mostly the season. Last November it took 240,000, so year over year, revenue grew (288,000 − 240,000) ÷ 240,000 = 20%. Against last November, spend rose from 48,000 to 64,000, +33%, and ROAS fell from 5.0 to 4.5.

Not to be confused with

  • Seasonal index — the shape of one year, month by month. YoY compares the same point in two years.
  • Detrending — removes growth to show the season. YoY removes the season to show growth.

Right and wrong readings

  • Wrong: “Revenue is up 20% year over year, so demand grew.” Right: in the example spend grew 33% and ROAS fell: the extra revenue came with extra budget.
  • Wrong: “November against last November is like for like.” Right: November 2025 had 10 weekend days, November 2026 has 9, and Cyber Monday fell on 1 December 2025 but falls on 30 November 2026. Going back 364 days keeps weekdays aligned; holidays still need a check.

Sources