Methodology
Bonus EV Methodology
Where the numbers in the bonus calculator come from. A walk through the expected-value math behind every casino welcome offer.
- Expected value (EV) = bonus value minus the expected loss to clear wagering at the house edge of your chosen game.
- Wagering volume = bonus × wagering multiplier ÷ game contribution rate.
- Most welcome bonuses are -EV by design - the wagering requirement is calibrated so the operator wins on average. A handful are +EV; the calculator tells you which.
The basic formula
Every casino bonus has three inputs that determine its real value:
- Bonus amount - the cash credited to your bonus balance.
- Wagering requirement - how many times the bonus (or bonus + deposit) must be wagered before any winnings become withdrawable.
- Game contribution rate - what percentage of each bet on the chosen game counts toward clearing wagering. Slots usually 100%; blackjack often 10%.
From those, plus the house edge of the game you'll play, the expected value of the offer is:
Where effective wagering volume is:
If EV is positive, the bonus is +EV - over many repetitions of the offer, you'd profit. If negative, the bonus is -EV - the wagering destroys more value than the bonus creates.
Worked example: a typical UK welcome bonus
Offer: 100% match up to £100, 35× wagering on the bonus, slots only (100% contribution), 30-day clearing window.
Inputs:
- Deposit: £100
- Bonus: £100
- Wagering: 35× bonus = £3,500 of slot play required
- Game: medium-volatility slot at 96% RTP → 4% house edge
- Game contribution: 100% (slots) → no adjustment
Expected loss while clearing: £3,500 × 4% = £140.
Expected value: £100 (bonus) − £140 (clearing cost) = −£40.
This is a -EV bonus. On average, taking this offer costs £40 over and above your deposit. Most UK welcome bonuses fall in this range. The bonus is real, but the wagering eats more than the bonus creates - you're paying the casino for the entertainment of a longer session.
What pushes a bonus into +EV territory
- Lower wagering multiplier. The same £100 bonus at 15× wagering needs only £1,500 of play - expected loss drops to £60 against the £100 bonus. EV = +£40.
- Lower-house-edge game. If the bonus terms allow blackjack with a 100% contribution rate (rare but possible at some live-dealer offers), the house edge drops from 4% to 0.5% - even at 35× wagering, expected loss is just £17.50. EV = +£82.50.
- No-wagering free spins. Spin winnings paid as cash with zero wagering have EV equal to the expected winnings minus zero. PlayOJO and a handful of other UKGC operators pioneered this.
- Cashback. A 10% cashback on net losses converts a -4% house edge into a -3.6% effective house edge over the cashback-eligible period. Compounds genuine value.
What makes a bonus catastrophically -EV
- Low game contribution on the only games you'd actually play. "£500 bonus, 35× wagering" sounds reasonable. "Blackjack contributes 10%" multiplies your effective wagering requirement by 10: £500 × 35 ÷ 0.10 = £175,000 of play to clear. At 0.5% house edge that's £875 expected loss against a £500 bonus. EV = −£375.
- Max cashout caps. If a £100 bonus caps your maximum withdrawal at £100, you can never realise the upper-tail wins that compensate for the variance of clearing. Expected value collapses toward the cap.
- Time limits that force higher bet sizes. If you have 7 days to clear £3,500 and your normal session is 100 spins, you need 100x more spins per session - most players will bet larger to compensate, raising variance and the chance of busting before clearance.
- "Bonus + deposit" wagering. If both bonus and deposit must be wagered (common at offshore casinos), effective wagering doubles. EV roughly halves.
Why variance matters even when EV is fixed
EV is the average across many repetitions of the offer. Any single attempt can finish far above or below EV depending on variance. For a -EV bonus, high-variance games can paradoxically increase your probability of finishing in profit on any one attempt - the wide outcome distribution pushes more of the right tail above zero. The cost: more sessions bust the bonus before clearing.
The calculator runs a 50,000-session Monte Carlo simulation to estimate not just EV but also the probability of profit on any one attempt, the median outcome, and the probability of busting the bonus early. Those numbers are what actually matter for the decision, not just the EV headline.
Bottom line
The expected value of a casino bonus is a function of four numbers: bonus amount, wagering multiplier, game contribution rate, and the house edge of the game you play. Three of those four come from the bonus T&Cs and you have no control over them. The fourth - game selection - is the only lever you can pull.
On a -EV bonus, switching from slots to live blackjack (where allowed) cuts your expected loss by roughly 8x. On a +EV bonus, the same switch maximises your guaranteed profit. Either way, the bonus calculator does the math - use it before depositing.