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Ever wondered whether that “just one more spin” is really worth it, or if the dealer is truly stacked against you? Good news: you don’t have to be a maths professor to work it out. Armed with a couple of quick rules of thumb—and, when you fancy, a pocket calculator—you can discover the real cost (or value) of any wager the casino puts in front of you.

Why “True Odds” Matter

The number printed on the felt is the payout, not the probability.
True odds are what you get when you crunch the actual chance of winning versus losing. The gap between the two is the house edge—effectively the casino’s commission for hosting the game.

Knowing the edge lets you:

Pick the cheapest games at your favourite UK online casinos.
Decide whether those shiny free spins or deposit match bonuses are worth a punt.
Spot “sucker bets” before they devour your bankroll.

The No-Calculator Method (Pub-Napkin Maths)

List every equally likely outcome.
– A single-zero roulette wheel has 37 pockets; two six-sided dice have 36 combos, and so on.
Count your winners.
– Example: betting red in roulette = 18 winning pockets.
Create the fraction.
– 18/37 ≈ 0.486.
Flip it to odds against.
– Losses : wins → (37 − 18) : 18 = 19 : 18.
Compare with the payout.
– The table pays 1 : 1, but true odds are 0.973 : 1, leaving a 2.7 % house edge.

Handy mental shortcuts

Task	Cheat code
European roulette even-money bets	Edge is always 1/37 ≈ 2.7 %
American roulette (0 & 00)	Edge doubles to 1/19 ≈ 5.3 %
Craps Pass Line	Remember “one-and-a-half” → ≈ 1.4 %
Baccarat	Banker ≈ 1.06 %, Player ≈ 1.24 %, Tie ≈ 14 %

The Calculator (or Spreadsheet) Route

When hand-waving isn’t enough—think blackjack strategy tables or video-poker pay-schedules—crack out the tech:

Enumerate outcomes programmatically.
Python’s itertools.product lists all dice or card combinations in seconds.
Score each outcome as +1 (win) or –1 (loss).
Average the scores to get expected value (EV).
EV − 1 = House edge.

Worked Examples

Roulette

Single number, single-zero wheel

Probability = 1/37
True odds = 36 : 1
Pays = 35 : 1
House edge = 2.70 %

Grab the American wheel instead and the edge leaps to 5.26 %—reason enough to stick to European rules on roulette tables.

Craps

Pass Line (no odds)

EV = –7/495
Edge = 1.41 %

Take double odds behind your bet and the blended edge plunges below 0.6 %. That’s as cheap as table games get.

Blackjack

Six-deck shoe, dealer stands on soft-17, basic strategy

Edge ≈ 0.5 %

Tweak one rule—say, 6:5 naturals—and the edge balloons to >1.5 %. Always skim the rule card before you pull up a seat at a blackjack table.

Baccarat

Eight decks, 5 % commission on Banker wins

Bet	Win %	Net payout	Edge
Banker	45.843	0.95 : 1	1.06 %
Player	44.615	1 : 1	1.24 %
Tie (8 : 1)	9.543	8 : 1	14.36 %

Hence the wisdom: back Banker, ignore the Tie—especially if you’re comparing tables at baccarat sites.

Video-poker & Slots

A “full-pay” 9/6 Jacks-or-Better machine returns 99.54 % to perfect play. Modern slots, by contrast, hover between 94 – 97 % RTP (edge 3 – 6 %). Unless you value flashing lights over long-term value, the numbers speak for themselves.

Putting it All Together

Know the edge, then decide whether the entertainment justifies the cost.
Use promotions wisely: free spins on a 96 % slot can be genuinely free EV if the wagering is fair.
Keep records. Logging stakes and results shows whether variance or house edge is driving your bankroll.
Bankroll discipline beats clever maths when the run goes cold.

How to Calculate Your True Odds in Casino Games (With and Without a Calculator)