How a published RTP figure is actually derived
RTP is not measured by watching players. It is calculated in advance from a game's own rules and payouts — and where those rules are public, the calculation can be checked line by line.
RTP is calculated, not observed
RTP is calculated, not observed. The method is the same for every game: list every possible outcome, its probability, and what it pays; multiply probability by payout for each outcome; add the results. That sum, expressed as a share of the amount staked, is the RTP. Nobody has to play a single spin for the number to exist.
Single-zero roulette makes the working visible
Single-zero roulette makes the calculation visible, because the rules are the whole game. A wheel has 37 pockets, each equally likely, and a straight-up bet has a 35-to-1 payout — a winning $1 bet returns $35 in winnings plus the $1 stake back, or $36 total. The expected return per $1 staked is (1/37) × 36, which is 36/37, or 97.2973%. Every standard bet on that wheel reduces to the same fraction, because every standard payout is set to match its own probability of losing, not its probability of winning.
Add one pocket and the arithmetic changes completely. Double-zero roulette has 38 pockets with the same 35-to-1 payout, so the same calculation gives 36/38, or 94.7368% — a house edge that has nearly doubled, from 2.70% to 5.26%, on a wheel that looks almost identical. The five-number bet on that wheel (0, 00, 1, 2, 3) breaks the pattern on purpose: its payout does not match its probability, and it returns only 35/38, or 92.1053% — the worst bet at that table, on the same wheel as every other bet's 94.7368%.
A slot is the same method with hidden inputs
A slot machine's RTP is calculated the same way — a weighted sum over every symbol combination and its payout — but the inputs usually are not public. The reel weights and the paytable are the manufacturer's own configuration, set per build, and a studio can and does ship several different RTP configurations of what looks like the same title. Roulette has one wheel and one set of odds anyone can read off the felt; a slot has a paytable that only the studio and the operator can see.
That difference is why this site's RTP records are short and roulette-heavy. A figure is published here only when the derivation can be shown in full, from rules that are actually public. A number with no visible derivation is an assertion, not a fact, and this site does not publish one it cannot show the working for.
To see what an RTP assumption does to a wagering requirement, use the expected balance calculator. To see how widely results scatter around it, use the variance explorer.