Online casino bonuses look generous on the homepage. A 100% match or a stack of free spins suggests free money, but the real value sits in the small print, and most players never run the numbers. This guide covers the costs that are rarely shown up front and the calculations worth doing before you claim anything.
Why the headline offer is not the real offer
A bonus is a promise with conditions attached. You receive extra funds or spins, but you must meet the terms before you can withdraw what you win. Those terms, not the percentage on the banner, decide what the offer is worth. The UK Gambling Commission explains that bonus funds are restricted, and its guidance on free offers and bonuses sets out what players should check before accepting one.
Wagering requirements: the cost that hides in plain sight
A wagering requirement states how many times the bonus, or the bonus plus deposit, must be bet before withdrawal is allowed. A £100 bonus with a 40x requirement means £4,000 in total bets. Because the house edge applies to every wager, you should expect to lose a share of that turnover before you can cash out. Since January 2026, operators licensed by the UK Gambling Commission have been barred from setting bonus wagering requirements above 10 times, so the same £100 bonus would carry at most £1,000 in required bets there. Offers from operators licensed elsewhere can still use far higher multipliers. Comparison platforms such as Casinous can help you line up different operators in one place, but the bonus terms on each operator’s own page are the ones that count: casinous.com.
Calculating the expected cost of a bonus
A simple way to estimate cost is to multiply the required turnover by the share of each bet the game is expected to keep. If a slot has a return to player (RTP) of 96%, the expected loss on every £1 wagered is about 4 pence. The formula is: required turnover × (1 − RTP). The table below applies it to common offers.
These figures are estimates. Short-term results vary widely, and the calculation ignores bet size limits and game restrictions. Still, it shows that a bonus can cost more in expected losses than the amount it adds to your balance.
Game contribution and maximum bet rules
Not every game counts equally toward a wagering requirement. Slots often contribute 100%, while table games may contribute 10% or be excluded altogether. If a 40x requirement on a £100 bonus only counts 10% from blackjack, you would need £40,000 in table bets to clear the same £4,000 target. Many terms also cap the stake you can place while bonus funds are active, often at a few pounds per spin. Going over that limit can void the bonus and any winnings linked to it, so read the rules before you play a single hand.
Time limits and the cost of rushing
Most bonuses expire within a set window, commonly seven to thirty days. A short deadline pushes players to speed up their play, raise their stakes, or chase losses to meet the target in time. Each of those choices increases the chance of losing the deposit itself. Mobile apps make this easier to do without noticing, since bonus timers and balances sit one tap away from every other feature.
Withdrawal caps and what you keep
Some offers cap the amount you can withdraw from bonus winnings, so a large win may be reduced to a fixed maximum. Before you accept, check whether your own deposit is still available if you stop playing. The Competition and Markets Authority’s do’s and don’ts for online gambling promotions states that firms should let customers exit a promotion at any time with their remaining deposit, plus any winnings earned from play with that deposit. Anything less than that deserves a closer look.
Comparing offers before you claim
Before claiming any offer, work through a short checklist:
- Write down the bonus amount and the wagering multiplier, then calculate the total turnover.
- Estimate the expected loss using the game’s RTP.
- Confirm which games count toward the requirement and at what percentage.
- Note the maximum bet allowed while bonus funds are active.
- Check the expiry date and any cap on bonus winnings.
- Save screenshots of the terms at the time you claim.
Treat the bonus as a cost, not a gift
A bonus only has value if you would have been willing to play that turnover with your own money at the expected loss shown in the calculation. If the numbers do not work on paper, the offer is probably not worth the time it takes to clear it. Gambling should be treated as paid entertainment with a budget you can afford to lose. If it stops feeling fun or starts to cause money problems, step back and seek support from a local gambling help service.