The most common math error is taking total member revenue and calling it "loyalty revenue." Wrong — those customers would have bought anyway. Loyalty ROI is the incremental revenue, not the total.
How to compute it correctly
- Measure your repeat purchase rate during a control period (3 months pre-launch).
- Launch the program and measure the same metric for 3 months.
- Delta × average basket = incremental revenue.
- Subtract costs (rewards redeemed + platform fee + campaigns).
- What's left is your real ROI.