Bonus funds are promotional money a casino adds to your account. You can stake them on eligible games, but you cannot withdraw them, or winnings from them, until the bonus terms are met.
Most sites keep bonus funds in a separate balance from your own cash. The terms say which is used first; many use real money first, so your own deposit is at risk before the bonus is touched. If you withdraw before wagering is complete, the bonus and its winnings are usually forfeited.
The conditions to look for are the wagering requirement, capped at 10x on GB casino bonuses since 19 January 2026, game weighting, any max bet rule, expiry, and whether the bonus is cashable. See bonus rules.