What a trifecta key covers
A key puts one horse in a fixed finishing position and lets the other horses fill the remaining positions in any order. The usual version keys a horse to win over several others for second and third. Keying one horse over N others covers N × (N − 1) combinations, because each of the N others can take second and the remaining N − 1 can take third. The calculator above is set to a key ticket; change the number of other horses to see the cost move.
Key versus box: the cost difference
A box covers every order of every horse, including orders where your top horse does not win. A key cuts those orders away, which makes the ticket cheaper but means it loses outright if the keyed horse is not in the position you chose.
| Other horses (N) | Key combinations | Key cost at $1 | Key cost at $0.50 | Box of N + 1 horses |
|---|---|---|---|---|
| 3 | 6 | $6.00 | $3.00 | 24 combinations |
| 4 | 12 | $12.00 | $6.00 | 60 combinations |
| 5 | 20 | $20.00 | $10.00 | 120 combinations |
| 6 | 30 | $30.00 | $15.00 | 210 combinations |
When a key makes sense, and when it does not
A key is a way to express a strong opinion about one position while covering uncertainty about the rest. It is only as good as that opinion and the price. A heavy favorite keyed on top may lower the payout so far that the ticket does not pay for the other combinations. If the price on the keyed horse is poor, the honest answer can be to pass. The GAMELIN read separates the projected winner from the price test for exactly this reason. See when to pass and overlays and underlays.
This tool counts cost, not payout
It does not estimate what a trifecta pays or recommend a ticket. The payout depends on the trifecta pool and the combination that finishes. Minimum bases, offered pools and coupled-entry rules vary by track, so confirm them before betting, and keep the total within a limit you set beforehand. Read the finishing-order guide for definitions, or the responsible play page.
Common questions
Is a key the same as a part wheel?
A key is a part wheel with one horse in one position. A part wheel can place several horses in each position. Use the style selector in the calculator to price either.
Can I key a horse to finish second or third?
Yes. A key in second or third over N others still covers N × (N − 1) combinations. Choose the key position in the calculator.
Sources and scope
Official references and GAMELIN's published evidence. Check current track and operator information before acting.