Promo weeks inflate velocity. The question buyers ask is not "how high did you spike?" but "where did you land afterward?"
We chart four post-promo weeks against the twelve-week pre-promo baseline. SKUs that settle above baseline earn repeat promo slots. SKUs that drop more than 30% below baseline get flagged amber in the chart book.
Presentation tip
Print the decay curve on A3 with the promo window shaded in tobacco brown. Buyers scan it faster than slide animations. Bring the underlying week table as a backup appendix—some category managers still ask for raw numbers.
Limitations we state upfront
Decay analysis needs clean baseline weeks. If you promoted three times in eight weeks, the baseline is unreliable and we say so in the footnote rather than forcing a curve.