In short
Last-click attribution gives all conversion credit to the final touchpoint before the conversion. It is simple, easy to explain, and still the default lens in many reports, which is exactly why it is worth understanding its bias. By crediting only the last click, it systematically undervalues upper-funnel work, awareness campaigns, and any touchpoint that opened the journey but did not close it, so budgets optimized purely to last-click tend to over-invest in bottom-of-funnel capture and starve the demand that fed it. This is why the major platforms moved their defaults to data-driven models. Last-click is not useless, because it is a clear, stable benchmark and a reasonable lens for tightly bottom-funnel campaigns. The risk is treating it as the whole truth. Read alongside a value-based or data-driven view, it becomes one perspective among several; read alone, it quietly rewards the campaigns that happened to be last rather than the ones that did the persuading.
Why it persists
Last-click is easy to compute, easy to explain, and consistent across tools, which keeps it alive in finance reports long after platforms abandoned it as a bidding input.
Where it misleads
Brand search and retargeting clicks sit closest to the conversion, so last-click inflates them and starves the awareness and consideration work that filled the funnel. Compare channels under a data-driven lens before cutting anything upper-funnel.
How does last-click attribution mislead budget decisions?
A brand judged its search-brand campaigns as top performers under last-click, then found that pausing upper-funnel spend shrank branded search itself. The last click was capturing demand created earlier, not creating it.
Reference: Google Ads Help, about attribution models