AFL multis: the real maths
A multi multiplies everything — the odds, the probability of losing, and the bookmaker's cut. That's not a reason never to have one; it's the reason to understand exactly what you're holding before you do.
How a multi is priced
Each leg's decimal odds multiply together. Four favourites at $1.50, $1.60, $1.70 and $1.80 combine to 1.5 × 1.6 × 1.7 × 1.8 = $7.34. Feels like turning four boring prices into one exciting one.
But probabilities multiply too. If those legs are genuinely 63%, 59%, 56% and 53% chances, the multi lands 0.63 × 0.59 × 0.56 × 0.53 = 11% of the time. You hold a ticket that loses nine weeks out of ten — by design.
The margin multiplies as well
| Legs | Effective margin (≈5%/leg) |
|---|---|
| Single | ~5% |
| 2 legs | ~10% |
| 4 legs | ~22% |
| 6 legs | ~34% |
| 10 legs | ~63% |
The 10-leg "$2 into $800" screenshot multi is, mathematically, one of the worst-value products in sports betting. It occasionally paying out is what keeps it sold.
Can a multi ever be value?
Yes — with one strict condition: every individual leg must be value on its own. If a model rates each side higher than its de-vigged market probability, multiplying legs multiplies the edge as well as the margin. Two legs with genuine +6% edges compound into a bigger combined edge than either single. This is the logic behind FootyAI's round value multi:
- Only legs where model % > market % after removing the vig — never "she'll be right" filler legs.
- Each leg must be a plausible winner in its own right (a minimum model probability and a maximum price) — positive edge on rank outsiders composes into absurd tickets that almost never land.
- Independent games only — one game's result can't rescue another leg.
- Few legs. Two or three good ones beat six ordinary ones, every time, because the margin compounds against you with each add.
Multi rules worth keeping
- Never add a leg to round the number up. "It's already $4.80, one more makes it $6" is precisely how the bookmaker wants you thinking.
- Same-game multis carry the fattest margins — correlated legs are priced defensively. Treat them as entertainment only.
- Expect long droughts. Even a genuinely value 3-leg multi at 20% only lands one week in five. Stake sizes should assume the drought, not the hit — see betting responsibly.
One multi. Every leg justified.
FootyAI composes the round's positive-edge legs into a single value multi — and shows the combined model %, market % and edge, so you can see exactly why each leg is there.
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