A '£50 bonus, 5x wagering at min odds 1.5' means you must place £250 of qualifying bets before the bonus converts to withdrawable cash. Every forced bet pays the bookmaker's margin, so the true cost of clearing is roughly turnover × margin: the headline number shrinks with each required spin through the book.
Rollover is the single most important line in any bonus's terms — far more than the headline amount. A small bonus at 1x wagering routinely beats a big one at 10x. Watch the supporting clauses too: minimum odds (higher minimums force riskier clearing bets), market exclusions, maximum stake per bet, and expiry dates that quietly void unfinished bonuses.
£40 bonus, 8x rollover, ~5% average margin: expected clearing cost ≈ £320 × 5% = £16. The bonus's realistic value is nearer £24 than £40 — and negative if a 7-day expiry forces sloppy bets.