Last-click attribution
Last-click attribution credits the final ad click before conversion with 100% of credit. The default model on most ad platforms; systematically over-credits bottom-funnel.
What does Last-click attribution actually mean?
Last-click attribution is the simplest and oldest attribution model: the final ad click before a conversion gets 100% of the credit. Every platform-reported ROAS uses last-click as the default unless you switch to a different model (data-driven, position-based, time-decay).
The well-known weakness: last-click systematically over-credits bottom-funnel touches and under-credits top-funnel ones. A user who saw a TikTok ad, searched the brand on Google, then clicked a Meta retargeting ad before purchasing is fully credited to Meta, even though TikTok did the awareness work that made the eventual conversion possible.
Despite the flaws, last-click remains useful for in-platform optimization (Meta's algorithm needs to credit something to learn from). The fix is to keep last-click and triangulate it with other measurement methods (DDA, MMM, incrementality testing) for budget allocation decisions.
Example
A user sees a TikTok ad, searches the brand on Google, clicks a Meta Reels ad, then converts. Last-click credits Meta with 100% of revenue. A holdout test would reveal Meta's actual incrementality is much lower.
When it matters
Last-click is fine for in-platform optimization. For budget allocation, supplement with DDA, MMM and incrementality testing, because last-click alone systematically overweights BOFU.
Related terms
DDA
DDA is Google's ML-based attribution model that distributes credit across touchpoints based on observed conversion paths in your account.
Attribution
Attribution determines which ad touchpoint receives credit for a conversion, using last-click, first-click, time-decay or data-driven models.
Incrementality
Incrementality measures the additional revenue ads generate vs. what would have happened without them, usually measured via holdout tests or geo-experiments.
View-through conversion
A view-through conversion is credited when a user sees an ad without clicking it, then converts within the attribution window.
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