A Buy bet wagers that a chosen box number—4, 5, 6, 8, 9, or 10—will roll before 7. Unlike a Place bet, it pays the number’s true odds. In exchange, the casino charges a commission, usually called the vig.
The most favorable common rule charges a 5% commission only when the bet wins. Under that rule, buying 4 or 10 is usually much better than placing it, buying 5 or 9 can also be better, and buying 6 or 8 is normally worse than placing them.
The wager itself is simple
Once accepted, the Buy bet remains on the chosen number until one of three things happens:
- the number rolls first and the bet wins;
- 7 rolls first and the bet loses;
- the player removes or reduces the wager before a deciding roll, if the applicable rules allow it.
The puck does not create the contract. The number-versus-7 race does. On many tables, Buy bets are off during the come-out roll unless the player calls them working and the dealer confirms that status. House procedure controls this, so the player should ask rather than assume.
| Number bought | Ways number rolls | Ways 7 rolls | True-odds profit |
|---|---|---|---|
| 4 or 10 | 3 | 6 | 2 to 1 |
| 5 or 9 | 4 | 6 | 3 to 2 |
| 6 or 8 | 5 | 6 | 6 to 5 |
A $20 Buy 4 therefore earns $40 before commission when 4 appears before 7. A $20 Buy 5 earns $30 before commission. A $30 Buy 6 earns $36 before commission.
True odds alone have zero expected value
Let:
- (w) be the number of dice combinations that make the selected number;
- 6 be the combinations that make 7;
- (t=6/w) be the true-odds profit multiple.
The win probability in the number-versus-7 race is:
[ P(win)=\frac{w}{w+6} ]
The loss probability is:
[ P(loss)=\frac{6}{w+6} ]
Without commission:
[ EV=P(win)t-P(loss) ]
Because (t=6/w), the two sides cancel. The commission is the entire casino advantage on a conventional Buy bet.
Commission charged only on a win
Suppose the vig is a fraction (c) of the amount wagered and is collected only after a win. The net win profit is (t-c) stake units.
[ EV=P(win)(t-c)-P(loss) ]
The true-odds portions cancel, leaving:
[ EV=-P(win)c ]
So the house edge is:
[ HE=P(win)c ]
At a 5% commission rate:
| Buy number | Win probability | House edge with 5% vig on wins |
|---|---|---|
| 4 or 10 | (3/9) | 1.6667% |
| 5 or 9 | (4/10) | 2.0000% |
| 6 or 8 | (5/11) | 2.2727% |
The same advertised “5% vig” creates different house edges because commission is collected only when the bet wins, and the six box numbers win at different rates.
Worked payouts using clean units
$20 Buy 4
True-odds profit:
[ $20\times2=$40 ]
Commission at 5% of the wager:
[ $20\times0.05=$1 ]
Net profit is $39, and the original $20 is returned. The bet’s expected result per decision is:
[ \frac{3}{9}(39)-\frac{6}{9}(20)=-$0.3333 ]
That is 1.6667% of the $20 stake.
$20 Buy 5
True-odds profit is $30. After $1 commission, net profit is $29.
[ \frac{4}{10}(29)-\frac{6}{10}(20)=-$0.40 ]
House edge is 2%.
$30 Buy 6
True-odds profit is $36. Exact 5% commission on the $30 wager is $1.50, leaving $34.50 profit.
[ \frac{5}{11}(34.50)-\frac{6}{11}(30)=-$0.6818 ]
House edge is 2.2727% before any unfavorable commission rounding.
Buy versus Place: the number decides
The comparison must use the same number and the same amount of action.
| Number | Common Place-bet edge | Buy edge with 5% vig on wins | Usually cheaper choice |
|---|---|---|---|
| 4 or 10 | 6.6667% | 1.6667% | Buy |
| 5 or 9 | 4.0000% | 2.0000% | Buy, if the vig rule is favorable |
| 6 or 8 | 1.5152% | 2.2727% | Place |
This is why “always buy every number” is poor advice. True odds sound attractive, but commission can make the resulting price worse than the ordinary Place payout.
The Place 4 and 10 guide explains the large improvement on those numbers. The Place 6 and Place 8 guide shows why their standard 7-to-6 payout is already efficient enough that a 5% Buy commission usually hurts.
The break-even vig rate is different for each number
Because an on-win commission is collected only when the number beats 7, the maximum commission that still beats the corresponding Place wager can be calculated. If (h_P) is the Place-bet house edge and (p_W) is the Buy bet’s win probability, the break-even commission rate is:
[ c^*=\frac{h_P}{p_W} ]
Using common Place payouts:
| Number | Break-even on-win commission rate | Meaning |
|---|---|---|
| 4 or 10 | 20.00% of stake | A normal 5% vig leaves a wide advantage for buying |
| 5 or 9 | 10.00% of stake | Buying still wins at 5%, but rounding can narrow the gap |
| 6 or 8 | 3.33% of stake | A 5% vig is already too expensive compared with placing |
This threshold calculation is more useful than the slogan that true odds are always best. The payout is fair before commission; the fee decides whether the final product beats the alternative on the layout.
Commission charged up front changes the answer
Some tables collect the vig when the Buy bet is made rather than only after a win. If 5% of the wager is charged on every decision, the expected commission is no longer multiplied by the win probability. Ignoring rounding, the cost is 5% of the wager each time the bet is resolved.
That rule has very different consequences:
- Buy 4 or 10 at a 5% every-time cost can still be cheaper than placing at 6.67%;
- Buy 5 or 9 at 5% becomes worse than placing at 4%;
- Buy 6 or 8 becomes much worse than placing at 1.52%.
A player who asks only “Is the vig five percent?” has not asked enough. The necessary question is: five percent of what, and collected when?
Rounding can dominate a small wager
Physical chip denominations rarely support every exact commission amount. A nominal 5% fee on $25 is $1.25. If the approved procedure rounds that to $2, the effective commission is 8% of the stake. If it rounds to $1, it is 4%.
The effect is most visible at low stakes. A $1 commission on a $10 Buy bet is 10%, not 5%. The table may therefore require specific Buy-bet increments or minimum amounts so the vig can be handled consistently.
Before betting, confirm:
- whether vig is charged on placement or only on a win;
- whether it is based on the wager or the amount won;
- how fractional commission is rounded;
- which bet increments the table accepts;
- whether the commission is included in the amount announced or paid separately.
Official rules illustrate why the posted procedure matters. Colorado’s craps regulation permits true-odds Buy bets and allows a commission based on the amount wagered, capped at five percent, while setting the corresponding true-odds payouts. See the Colorado rules for craps Buy bets and payout odds. Other jurisdictions and casinos may approve a different collection or rounding method.
What the dealer is doing with the chips
A Buy bet is normally positioned by the dealer in the box for the selected number and marked so it is not confused with an ordinary Place wager. The marker, chip orientation, or placement convention varies by house.
The crew must track:
- whose wager is on each number;
- whether it is Buy or Place;
- whether commission has already been collected;
- whether the bet is working on the come-out roll;
- the correct true-odds payout and vig;
- any increase, reduction, press, or removal requested before the decision.
Players can reduce disputes by stating the full instruction: “Buy the 4 for $20, vig on win?” is clearer than pushing chips toward the dealer and saying only “four.”
Pressing changes future action, not the completed payout
Suppose a $20 Buy 4 wins and earns $39 after commission. The player asks to press to $40. The completed $20 wager has already settled. The dealer leaves or moves $40 as the new Buy amount and returns the balance according to house procedure.
The new wager has its own commission calculation. Pressing does not make the previous win larger; it increases the money exposed to the next 4-versus-7 race.
If the $40 Buy 4 uses a $2 vig on win, a winning decision earns $78. A losing 7 removes $40. The edge percentage is unchanged under proportional commission, but expected dollars lost per decision double with the stake.
A practical rule for choosing
Use Buy bets selectively rather than as a category-wide instruction:
- 4 and 10: buying is usually the clear mathematical improvement when vig is 5% and collected on wins;
- 5 and 9: buying can improve the price, but collection timing and rounding matter;
- 6 and 8: ordinary Place bets are normally cheaper under the common 5%-on-win Buy rule.
Then choose clean units that fit both the true-odds payout and the commission procedure. The craps odds calculator can verify the number-versus-7 probabilities, while the expected loss calculator can compare repeated Buy and Place action in dollars.