Most CPG sales teams evaluate promotions the same way: compare promoted weeks to non-promoted weeks, calculate the volume lift, and declare success if the number is positive. It's simple, intuitive, and dangerously incomplete.
Volume lift doesn't account for baseline cannibalization - the sales that would have happened anyway. It ignores forward buying - consumers stocking up at discount, depressing future full-price sales. It says nothing about margin erosion - whether the incremental volume actually generated profit after the trade spend and COGS are factored in. And it completely misses pantry loading, where you're effectively training consumers to wait for deals.
A promotion that lifts volume 30% can still lose money. If the cost of driving those extra units exceeds the margin they generate, you've got a net loss dressed up as success.
The question isn't "did volume go up during the promotion?" The question is "did this promotion generate more gross margin than it cost?"
Even brands that go beyond volume lift and calculate some form of incremental ROI are usually missing a critical piece: the margin erosion on base volume.
When you run a promotion, you don't just sell extra units at a discounted price. You also sell your baseline units - the ones that would have moved at full price - at that same discount. Traditional ROI only counts the gains on incremental units. It ignores the margin you gave up on units that were going to sell regardless. This gap between traditional and TRUE ROI can mean the difference between an event that looks profitable and one that's actually destroying margin.
This blind spot is why so many brands repeat the same underperforming promotions year after year. The numbers they're looking at don't capture the full economic picture.
The quality of any ROI measurement depends entirely on the baseline estimate. Get it wrong and every downstream metric is compromised. Simple approaches like comparing to non-promoted periods miss seasonality. Year-over-year methods break down when distribution or pricing changes. The reality is that accurate baseline estimation requires a thoughtful analytical framework that accounts for multiple demand drivers simultaneously.
The key insight is that consistency matters more than perfection. A methodology applied uniformly across all promotions gives you a reliable basis for comparing events even if the absolute numbers carry some estimation error. Consistent measurement reveals which promotions are relatively better or worse - and that's what you need for planning.
If you're evaluating your promotional performance, ask whether your current approach answers these questions:
If you can't answer these confidently, your ROI framework has gaps.
What you'll typically find when you analyze promotions rigorously is striking: a small number of events drive the majority of your incremental profit, while a significant portion are net-negative on margin. That insight alone tells you where to focus trade spend next year.
At Strata CPG, we automate this analysis across your full promotion history using our TRUE ROI analysis engine. Every event gets scored and classified, and those insights feed directly into AI-powered annual promo planning so that historical performance data drives forward-looking strategy.
The brands that measure promotions rigorously don't just optimize trade spend - they transform it from a cost center into a profit driver.