How to Calculate the True Value of Any Offer
Expected value (EV) is the single most important concept in bonus betting. It is the average outcome you would get if you repeated the same promotional claim hundreds of times — the mathematical heart of whether an offer deserves your bankroll. Without EV calculation, your claiming decisions depend on intuition and headline numbers. With EV calculation, every offer becomes a clear yes or no, ranked by return. This lesson gives you a step-by-step method for calculating what deposit matches, free bets, and casino bonuses are actually worth in cash before you commit to them.
What True Cash Value Means
Expected value (EV) is the average financial outcome of a decision if it were made repeatedly. A decision with a positive expected value (+EV) will, on average, make you money over time. A decision with a negative expected value (−EV) will, on average, lose you money over time. Bonus betting is the practice of identifying and exploiting +EV decisions within sportsbook and casino promotional structures.
The core EV formula for any wager is: EV = (Probability of winning × Amount won if you win) − (Probability of losing × Amount lost if you lose).
A typical sportsbook bet carries a negative EV because of the bookmaker's overround (their profit margin). A £20 straight bet at 2.00 odds might have a true 47.6% chance of winning. Over time, that bet loses money. But if that same £20 bet triggers a £30 free bet token, the combined mathematical package becomes highly positive EV. The promotion offsets the expected loss of the qualifying bet.
Calculating the Qualifying Cost
Before valuing the bonus itself, you must price the cost of obtaining it. The qualifying cost is the expected loss (EL) on the bet(s) required to trigger or clear the promotion.
Qualifying cost = Qualifying stake × Bookmaker margin at qualifying odds
You can find the exact margin for any odds pairing using our Overround Calculator. As a benchmark, heavily traded football match winner markets (1X2) typically carry a 4–6% margin.
Example: £20 qualifying stake at 5% margin → qualifying cost = £20 × 5% = £1.00
If the promotion requires qualifying bets at high minimum odds (e.g., 3.00+), the margins are typically worse. The same £20 bet placed at 8% margin would have a qualifying cost of £1.60. Always factor in the specific margin of the required qualifying market.
The Value of Free Bets (SNR vs SR)
Stake Not Returned (SNR) Free Bets
Most modern free bets are SNR: you receive the profit if the bet wins, but you do not get the free bet stake back. Because you don't keep the stake, SNR free bets are mathematically worth more when placed at higher odds.
Cash Value = Free bet stake × (Decimal odds − 1) × True win probability
Where true win probability = 1 ÷ Fair exchange odds.
Example: £50 SNR free bet placed at 4.00, true probability 25%:
Value = £50 × 3 × 0.25 = £37.50 (or 75% cash extraction)
As a rule of thumb: If placed at odds between 3.50 and 5.00, a £50 SNR free bet is worth roughly £35 to £40 in long-term EV. Use the Free Bet Calculator to model the exact value of any token.
Stake Returned (SR) Free Bets
SR free bets are rare but highly valuable. If the bet wins, you get the profit plus the original stake back. Because you retain the stake on wins, SR free bets retain roughly their full face value regardless of the odds you place them at. A £50 SR free bet is worth approximately £48–£50 in EV.
Calculating Deposit Matches
A deposit match (e.g., "100% matched up to £200") provides bonus cash subject to a rollover (wagering) requirement. To find the true cash value, you must deduct the cost of clearing that rollover from the face value of the bonus.
Expected Wagering Loss = Total rollover required × Average margin
Cash Value = Bonus amount − Expected Wagering Loss
Example: £100 bonus with a 5× wagering requirement on the bonus only. You choose markets with a 4% margin.
Total rollover required: £100 × 5 = £500
Expected Wagering Loss: £500 × 4% = £20
Cash Value: £100 − £20 = £80
A Great Deposit Match
£150 bonus, 3× wagering requirement. Average margin 5%.
Expected loss: £450 × 5% = £22.50
Cash Value: £150 − £22.50 = £127.50
A Toxic Deposit Match
£100 bonus, 10× wagering on deposit + bonus (£2,000 rollover). Margin 5%.
Expected loss: £2,000 × 5% = £100
Cash Value: £100 − £100 = £0
Evaluating Casino Bonuses (RTP & House Edge)
Sportsbook welcome offers often include bundled casino bonuses or free spins. Calculating their value requires understanding Return to Player (RTP) percentages. RTP is the long-term percentage of stakes returned to players as winnings. The House Edge is the remainder (100% − RTP).
If a slot game has an RTP of 96%, the house edge is 4%. This is identical to a sportsbook margin of 4%.
Expected Wagering Loss = Total rollover required × House Edge
Cash Value = Bonus amount − Expected Wagering Loss
Example: £50 casino bonus with a 20× wagering requirement on a 96% RTP slot (4% house edge).
Total rollover required: £50 × 20 = £1,000
Expected Wagering Loss: £1,000 × 4% = £40
Cash Value: £50 − £40 = £10
Free Spins
If an offer includes "50 Free Spins worth £0.10 each", the initial face value is £5.00. The long-term expectation of those spins is their face value multiplied by the game's RTP (e.g., £5.00 × 96% = £4.80). If the winnings from the free spins are paid in cash with no wagering requirements, their EV is exactly £4.80. If the winnings are paid as a bonus requiring more rollover, you must deduct the rollover cost using the casino formula above.
While the maths for casino EV is identical to sports EV, the variance curve on slot machines is extreme. A sports bet at 2.00 odds wins 50% of the time. A slot machine spin might return nothing 80% of the time, and a large payout 1% of the time. You may frequently bust (lose) the entire bonus before completing the rollover. This is expected — the EV formula measures the average long-term outcome across hundreds of bonuses, not the guaranteed result of one.
The Full Net Value Formula
When you encounter a welcome package that includes multiple components—such as a qualifying bet hurdle, a deposit match, and a bundle of casino spins—you simply calculate the value of each component and combine them.
Net Cash Value = Bonus Value + Additional Rewards Value − Qualifying Cost
Worked full example: "Bet £10, Get a £30 Free Bet + 50 Free Spins (No Wagering)"
• Qualifying bet: £10 at 5% margin → cost = −£0.50
• Free bet: £30 SNR placed at 4.00 odds → value = +£22.50
• Free spins: 50 spins at £0.10, 96% RTP, no rollover → value = +£4.80
Net Cash Value = £22.50 + £4.80 − £0.50 = £26.80
If the Net Cash Value (EV) is robustly positive, the offer is worth taking. By mapping the math out beforehand, you eliminate the guesswork and protect your bankroll from offers that look massive but harbour negative expectations beneath toxic wagering terms.
Common Questions
EV measures the average outcome over a massive sample size, not the outcome of a single attempt. Casino bonuses, especially high-volatility slots, will often result in the bonus busting (reaching £0) before the wagering is complete. This means you make £0 on that specific offer. However, on the rare occasions you do clear it, you might withdraw significantly more than the starting balance. Over 100+ positive EV casino offers, your actual return will closely match your calculated EV, but any single offer is highly vulnerable to variance.
The qualifying cost in the EV calculation already accounts for the expected average outcome of the qualifying bet (-margin). You don't need to try and guess whether the specific bet will win or lose. When calculating EV, you are only ever measuring mathematical expectation, not the eventual real-world result of the specific events you bet on.
High minimum odds (like 2.50 or greater) usually correspond with higher bookmaker margins (closer to 7–9%). This directly increases your Qualifying Cost and your Expected Wagering Loss. Whenever minimum odds are high, you must recalculate your EV to reflect the costlier margin. A £100 rollover at 1.50 minimum odds is much cheaper to clear than a £100 rollover at 3.00 minimum odds.
Now that you can calculate the true mathematical cash value of any promotion, it's time to map out how to execute these concurrently. The next lesson covers how to organise a multi-operator bonus campaign and track your portfolio effectively.
Next: Stacking Promos Across Multiple Books →