“Welcome bonus: get 150% up to £150 on your first deposit”. It’s the kind of offer that greets anyone who visits a British online betting site. What it doesn’t say is that if you decide to spend £50 on this offer, you’d need to stake an additional £750 of your own money before any winnings could be withdrawn.

Recent research by colleagues and I asked nearly 600 UK bettors to work out the true cost of exactly that kind of offer. Nearly everyone got it wrong, underestimating the real amount often by hundreds of pounds.

Financial inducements, “free” bets, deposit matches and welcome bonuses are a standard part of signing up with almost any UK operator. Their behavioural harms are well established. They encourage people to gamble more often, push bettors towards riskier wagers and are linked to chasing losses. The heaviest effects tend to fall on those already experiencing gambling harm.

But behaviour is only half the story. Harm can also stem from something more basic: not understanding what an offer actually requires of you in the first place. That’s where wagering requirements come in – the rules saying you have to bet the bonus amount a certain number of times over before any winnings attached........

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