The calculation, in one line
A wagering requirement is the multiple of a bonus you must wager before the balance becomes withdrawable. A 500 unit bonus at 40x requires 20,000 units of turnover.
That turnover is not free. At a house edge of 4%, wagering 20,000 costs 800 in expectation. You were handed 500.
Run that through the block below and the position is visible rather than argued:
Expected cost assumes you clear the wagering on games at the stated RTP and ignores maximum bet limits, game weighting and cashout caps, each of which makes the real figure worse. A negative expected net means the offer costs more to unlock than it hands you.
The offer costs more to unlock than it provides, before any of the secondary restrictions apply. That is the standard structure, not an unusually bad example.
The terms that make it worse
Bonus plus deposit. Some requirements apply to the bonus and the deposit together, which nearly doubles the turnover. Read whether the multiplier attaches to “bonus” or “bonus and deposit”, because the words are similar and the difference is enormous.
Game weighting. Slots typically count 100% toward clearing, table games often 10% or less. A blackjack player facing a 40x requirement at 10% weighting is effectively facing 400x.
Maximum bet during wagering. Usually capped at a small amount. Exceeding it once can void the bonus entirely, and the cap also stretches clearance over more bets, which increases total exposure to the edge.
Maximum cashout. Some bonuses cap what the bonus can win regardless of results. Turn a 20 bonus into 900 and withdraw 100, because that was the cap.
Expiry. A window forces volume into a short period, which raises the chance of busting before clearing.
When a bonus is worth taking
The maths is not always against you, and pretending otherwise would be as one-sided as the marketing.
A low multiplier changes the picture. At 20x rather than 40x, the same 500 bonus requires 10,000 turnover costing 400, which leaves you 100 ahead in expectation. Our list of lower-cost operators is a better starting point than a bonus table.
Small deposits also favour bonuses. If you are funding an account with 50 and playing one session, a matched deposit puts more in front of you than any rakeback will return on that turnover.
The threshold is roughly this: bonuses suit occasional small-stakes play, and continuous returns suit volume. Neither is universally better and any site telling you otherwise has not done the arithmetic.
The alternative model
Some operators skip bonuses and return part of the house edge on every bet instead. There is no requirement to clear, nothing expires, and the value arrives from the first wager.
Whether that beats a bonus depends entirely on how much you play, which is the calculation this page exists to make possible. Our review of one operator running that model works through the comparison with its actual terms.