Slot machines usually contribute 20% toward a bonus's playthrough requirement — sometimes 10%, occasionally zero. On a $200 slot bet, that means only $40 to $60 gets credited against the wagering you need to clear. The rest of the bet is real money moving through the machine, but it does nothing to unlock your bonus.
That gap is the single most expensive detail in most sign-up offers, and it's buried in the terms page nobody opens.
Why the 20% rule exists
Bonus cash is a liability. If a casino let you clear a $500 playthrough entirely on slots, you'd grind it out at a 96% RTP game, lose roughly $20 in expected value per $500 wagered, and walk with the difference. The house edge on slots is thin enough that a full-contribution rate would make bonuses a losing proposition for the operator.
So they weight games by margin. Slots get 20%, video poker gets 10% or less, blackjack and roulette often get 5% or nothing. Table games have a lower house edge per hand, so the casino needs more hands — or more dollars wagered — to extract the same expected profit. The contribution rate is a rough proxy for that math.
What $200 on slots actually does
Say you deposit $100 and get a $100 bonus with a 30x playthrough requirement on the bonus amount. That's $3,000 you need to wager before withdrawing.
At 20% slot contribution, every $200 you spin credits $40. To clear $3,000, you'd need to wager $15,000 in real bets. At 100 spins per hour on a $1 machine, that's 150 hours of play — assuming you don't bust first.
Here's the part that catches people: the contribution applies to wagers, not wins. A $200 spin that returns $180 still counts as $40 toward playthrough, not $36. The casino tracks total amount wagered, win or lose.
The games that actually clear bonuses
If your goal is finishing playthrough rather than chasing a jackpot, contribution rates matter more than RTP. A 97.3% RTP slot at 20% contribution is worse for clearing a bonus than a 96% slot at 100% contribution — if you can find one. Some casinos run "bonus-eligible" slot categories at full weight, usually older three-reel games with lower volatility.
High-volatility slots are a trap here. A 10,000x max win sounds great until you realize the variance means you might burn through your entire balance before reaching 30% of the playthrough target. Low-volatility slots with 96%+ RTP and full contribution are the boring, correct answer.
Also check the max bet rule. Most bonuses cap individual wagers at $5 to $10 while a bonus is active. Exceed it once and the casino can void your winnings — a $200 spin on a bonus balance would trigger that instantly.
Where this leaves you
The honest read: a $100 bonus with 30x playthrough at 20% slot contribution is worth less than the deposit you made to get it, in expected-value terms, for most players. The people who profit are running low-variance strategies on high-contribution games and treating the bonus as a small rebate, not a payday.
Which raises the question worth asking before your next deposit: if the terms are structured so that slots — the games most players actually want to play — are the worst possible way to clear the requirement, is the bonus designed to reward you, or to keep you spinning past the point where it made sense?
Set a loss limit before you deposit, not after.