A bonus headline tells you what you get. It does not tell you how much you have to stake to keep it, or what that staking costs on average. This calculator does both sums. Type in four numbers from the offer terms and it shows the total you must bet, the expected cost of that play, and what is left of the bonus once the cost is taken off.
It runs in your browser, stores nothing and needs no sign-up. The defaults show a 20 pound bonus at the legal maximum of 10x on a typical slot, so change them to match the offer in front of you.
The four inputs
Bonus amount. The bonus funds in pounds, not your deposit. For free spins with wagering attached, wait until the spins have finished and enter what they won, because the requirement applies to those winnings.
Wagering requirement. The multiple in the terms. The box will not accept more than 10, for the reason given further down.
Game RTP. The return to player of the game you plan to use. It is in the game's help or information screen. Check it there and not on a review site, because the same slot can run at different settings at different casinos. Many slots sit at around 96%, and some are set lower.
Game weighting. How much of each bet counts towards wagering. Slots are usually 100%. Roulette, blackjack and live games are often 10% or 20%, or excluded altogether. The table is in the bonus terms under a heading like "game contributions".
The formula, with a worked example
There are only two lines of arithmetic. Total stake is the bonus multiplied by the wagering requirement, divided by the weighting. Expected cost is the total stake multiplied by the house edge, which is one minus the RTP. Expected value is the bonus minus that cost.
| Slot, 100% weighting | Roulette, 20% weighting | |
|---|---|---|
| Bonus | 50 pounds | 50 pounds |
| Wagering | 10x | 10x |
| RTP | 96% | 97.3% |
| Total stake | 50 x 10 / 1.00 = 500 pounds | 50 x 10 / 0.20 = 2,500 pounds |
| Expected cost | 500 x 0.04 = 20 pounds | 2,500 x 0.027 = 67.50 pounds |
| Expected value | 50 - 20 = 30 pounds | 50 - 67.50 = minus 17.50 pounds |
Same bonus, same multiple, opposite answers. Roulette has the better RTP, yet the weighting forces five times as much play, and the cost overtakes the bonus. This is the sum that tells table players to turn down a slot-led offer.
Expected value is an average, not a promise
The 30 pounds in the first column is what the bonus would be worth per attempt if you could take it thousands of times. You cannot. You get one run, and one run on a slot is noisy. Plenty of players will lose the whole bonus balance before reaching 500 pounds of stakes. A smaller number will finish far ahead. The average of all those outcomes is 30 pounds, and almost nobody lands on it.
The calculator also leaves out terms it cannot know: a win cap, a maximum bet, an expiry date. Any of those lowers the real value. So treat the output as a way to compare two offers, or to spot one that costs more than it gives. It is not a forecast of what you will withdraw, and a bonus with a positive figure is still not a way to make money. Decide what you are happy to spend before you start, and set a deposit limit to match.
Why the wagering box stops at 10
Since 19 January 2026 the Gambling Commission has capped wagering on bonus funds at ten times. Before that, 35x and 40x were routine, and at those multiples the expected cost on a 96% slot was larger than the bonus itself. If a site is showing British players a figure above 10x today, it is not licensed here. Our wagering requirements guide covers the cap in full, and the glossary defines every term on this page.
When there is nothing to calculate
Set the wagering box to zero and the expected cost falls to zero as well. That is a no-wagering offer in one line: whatever the spins win is credited as cash, with no turnover to grind through, so the bonus is worth what it pays. Such offers tend to be smaller for that reason. Our bonus comparison shows which casinos run them.
Questions people ask
How do you calculate a wagering requirement?
Multiply the bonus by the wagering multiple, then divide by the game weighting. A 50 pound bonus at 10x on a game that counts 100% needs 500 pounds of bets. At 20% weighting it needs 2,500 pounds.
Why does the wagering box stop at 10?
Because 10x is the legal maximum. Since 19 January 2026 no casino licensed by the Gambling Commission may set a higher wagering requirement on bonus funds.
Is a positive expected value a guarantee of profit?
No. Expected value is the average across a very large number of attempts. A single run through a bonus can end with nothing or well ahead, and slots make the swings wide.
What should I enter for free spins?
Enter the amount the spins won as the bonus amount, since wagering on free spins applies to the winnings. If the spins have no wagering, there is nothing to calculate.