A welcome bonus is an offer a casino makes to new customers, typically bonus funds that match part of a first deposit, a set of free spins, or both. It always comes with terms.
The terms are where the value is decided. Look for the wagering requirement, which on GB-licensed casino bonuses has been capped at 10x since 19 January 2026; which games count and by how much (game weighting); any max bet rule while the bonus is active; time limits; and any cap on winnings.
A bonus does not change the house edge of the games you play with it. Wagering a bonus means staking it repeatedly, and the expected cost of that staking comes off its value. Since 19 January 2026, mixed-product offers such as "bet on sport to get casino spins" are also banned for GB customers.
Treat a welcome bonus as a small extra on play you would have done anyway, never as a reason to deposit. See bonus rules.