The formula
Example
A ₱3,000 promo brings 40 customers spending ₱220 each at 60% margin: profit ₱5,280, ROI 76%.
Be honest about "because of it"
Some customers would have come anyway. Compare with a normal week, or with similar customers who didn't get the message, and only count the extra.
In Selyo, each message shows how many customers came in within 7 days, a good starting point for this calculation.