Casino bonuses land in your inbox with a headline number on top and a block of terms underneath, and the headline number exists to catch your eye. A £100 bonus on a £20 deposit reads like free money. Claim it and you take on a wagering requirement that decides whether you finish ahead or behind. Work through that requirement first and you can tell in a few minutes whether an offer deserves your deposit, because the terms carry more weight than the size of the figure beside them.
Money you deposit sits in your cash balance. Money the casino adds sits in a bonus balance, and the operator locks that balance until you stake a set multiple of it. That multiple is the wagering requirement, written as 35x, 40x or 50x. A 35x requirement on a £50 bonus means £1,750 in bets before the bonus turns into cash you can withdraw.
Casinos count stakes rather than wins toward the requirement. You can bust the bonus balance on the way and finish with nothing, and the terms still credit every £1 you staked. Understanding how a casino bonus is built shows you where the lock sits and what it takes to open it.
Many operators also apply a cash-first rule. Your real money gets staked before the bonus money does, which keeps the bonus alive through a bad run and drains your deposit first. Check that clause before you claim, because it changes how long your own money lasts.
Take a £100 bonus with a 35x requirement. You need £3,500 in stakes. On a slot with a 96% return to player, the house keeps 4% of everything staked, so £3,500 in stakes carries an expected loss of £140. The bonus pays out £100. The average player finishes £40 down on the deal, and the house collects that £40 in small amounts across thousands of spins.
£100 bonus, 35x wagering, 96% RTP: £3,500 staked, £140 expected loss, £100 bonus paid, £40 down on average.
Change any number and the result moves. A 40x requirement on the same £100 lifts the expected loss to £160. A 30x requirement on a 97% slot drops it to £90, which sits below the bonus value and leaves you £10 ahead. The maths rewards patience with terms, and it punishes anyone who claims on the headline alone.
Your deposit counts in the calculation too. A £20 deposit with a £100 bonus and 35x wagering on the bonus gives you a £3,500 target. If the terms apply 35x to the deposit and the bonus together, the target climbs to £4,200 and the expected loss climbs with it.
A £10 bonus at 5x needs £50 in stakes and costs £2 in expected losses on a 96% slot, which leaves £8 of value in your hands. A £200 bonus at 65x needs £13,000 in stakes and costs £520, which buries the bonus under a £320 loss. Small bonuses with low multiples beat large bonuses with high ones, and the wagering figure tells you which is which before you stake a penny.
Most bonuses count slot stakes at 100% toward the requirement. Table games take a haircut. Roulette and blackjack often count at 10%, which stretches a 35x requirement into £35,000 of bets on a £100 bonus. A £100 bonus then needs £35,000 in roulette stakes before it unlocks, and how table game odds cut into a bonus matters more than the size of the headline figure.
Contribution rates also decide which games you can play without wasting the bonus. Spin £10 on slots and you clear £10 of the requirement. Spin £10 on roulette at 10% and you clear £1. Ten hours of roulette moves the same distance as one hour of slots.
Live dealer tables carry the same problem. Live roulette returns 97.3% to the player, which sits close to a slot's 96%, but the 10% contribution means you stake ten times as much to clear an identical requirement. The RTP looks comparable and the workload does not.
Operators do not hand out bonus money as a gift. They buy your play with it. The house edge does the work across thousands of stakes, and the wagering requirement keeps you betting long enough for the edge to collect its share. A £100 bonus that generates £3,500 in stakes earns the operator £140 on a 96% slot, which covers the bonus and leaves margin. That is the trade behind a welcome offer, and the arithmetic on what a welcome offer costs favours the operator by design.
None of this makes bonuses fraudulent or rigged. Operators publish the wagering figure and you accept it when you claim. The offer works as a bet on your discipline: they wager that you stake the full amount, you wager that variance lands on your side before the requirement clears.
Wagering £3,500 takes time. At £1 per spin on a slot running 20 spins a minute, you sit there for close to three hours. Variance decides whether the balance survives the trip, and a cold run can wipe the bonus balance before the requirement clears. You can stake the full £3,500 and withdraw nothing. Thinking through the maths of a session before you claim tells you how much of your own cash the wagering could consume.
Bankroll size matters more than spin size. A £50 bankroll against a £3,500 requirement runs out long before the bonus clears. A £500 bankroll with the same requirement survives the swings and lets you clear the requirement with something left over.
Four clauses in the small print change the result more than the bonus size. A max bet rule caps each wager at £5 and voids your bonus the moment you break it. A game exclusion list removes the titles you play most. An expiry window of seven days forces you to clear £3,500 in a week. A maximum win cap of £100 turns a large bonus into a small payout.
Bonus funds also vanish at the expiry date, so an offer you cannot clear in seven days carries no value. The terms page does not lead with the price you pay for a bonus, and a cap on winnings can leave you with less than you staked to reach it.
Five things to check: wagering multiple, game contribution rates, max bet cap, expiry window, maximum win cap.
Every UK casino holds a licence from the Gambling Commission, which covers the games and the payment terms, but the regulator does not standardise bonus conditions. Operators set their own wagering figures, and those figures range from 10x to 65x on comparable offers. Reading a FamBet Casino review takes five minutes and gives you the wagering requirement, the contribution rates and the expiry window before you deposit a penny.
Payment terms deserve the same check. Debit cards, PayPal and open banking transfers through Trustly clear in minutes, and UK operators stopped accepting credit cards for gambling deposits in April 2020. A withdrawal that stalls for two days while a bonus expires can cost you the balance you spent hours clearing.
A bonus works in your favour when three conditions line up: a low wagering multiple, full contribution on the games you play, and enough time to clear the requirement. A 10x requirement on a 97% slot costs about £30 in expected losses against a £100 bonus, which leaves you ahead on average.
Most welcome offers fail that test, and claiming one anyway turns a bonus into an extra cost. Treat the value as part of your entertainment budget rather than income. Set a deposit limit before you claim, watch the clock if the expiry window is tight, and use GamStop for a longer break if play stops being fun. BeGambleAware and GamCare run free support if you need someone to talk to.
