Gambling marketing is linked to increased intentions to gamble, gambling behaviours, and gambling spend. The researchers examined the link between unplanned gambling spend and gambling marketing among people who gambled in Britain. The researchers used data from two British online surveys. The first survey involved emerging adults aged 16–24 years old. The second survey involved adults who regularly bet on sports. In both samples, almost a third of participants said that marketing caused them to have unplanned gambling spend. Among people who experienced problem gambling, almost 9 in 10 said that marketing prompted unplanned gambling spend. Thus, the severity of problem gambling was linked to unplanned gambling spend. Receiving at least one form of direct marketing in the past month and following a gambling brand on social media were also linked to unplanned gambling spend. Being aware of marketing in the last month was not linked with unplanned gambling spend.