Welcome bonuses are marketing. Expected value is math. Plug in a bonus and see what it is actually worth once you have wagered it through. The calculator assumes you play slots at the RTP you pick. If you play blackjack correctly, the number is better; if you play any table game poorly, it is worse.
EV assumes slots-only play at the RTP above. Higher-RTP games raise the number. Table games with poor play lower it. Bonus T and Cs with low max bets and fast expiry lower it further.
Matched bonus is what the site credits after your deposit, capped by the bonus cap. Total wagering is that bonus (or deposit plus bonus, in a free-bet model) multiplied by the rollover. Expected loss is the house edge times the wagering. Expected net value is the matched bonus minus the expected loss. Positive numbers mean the bonus is, on average, worth taking; negative numbers mean you are paying for it.
A 1,000 USD bonus at 40x rollover requires 40,000 in wagers. At 96 percent RTP, the expected loss on that volume is 1,600. You are paying 600 for a 1,000 bonus. Any bonus where the rollover times (1 minus RTP) exceeds the match value is a losing trade. Most 100 percent bonuses at 40x fall exactly into that trap.
Game weighting (some games count less toward rollover). Max bet during bonus (breach it, lose it). Expiry windows (can't clear 40x in seven days without binary bets). Stake-returned free bets versus match bonuses (the model toggle handles this, roughly). Use the output as a directional number, not a contract.
Our guide to crypto welcome bonuses and glossary cover the jargon. Stake and BC.Game are the two operators where the rollover math tends to come out cleanest.