Incrementality is the portion of a program's results that would not have occurred without it, the sales, visits, or retention the program genuinely caused, as opposed to behavior that would have happened regardless. It isolates the program's real contribution from activity it merely observed.
Suppose members who receive an offer spend more than members who do not. Part of that gap may be the offer working, but part may be that the offer went to members already inclined to buy. Incrementality is only the difference the offer actually created, which is why measuring it usually requires comparing rewarded members against a comparable group held out from the treatment.
For an operator, incrementality is the honest test of program value and the hardest number to face. Rewarding purchases customers would have made anyway is pure cost dressed up as success, and headline figures like total redemptions or member spend routinely overstate impact. Programs that measure incrementality can tell which offers, tiers, and mechanics pay for themselves and redirect budget away from the ones that only appear to work, which sharpens the entire program's economics.
