AFL value betting means backing a price that is above what the selection is really worth, and the only way to know that is to work out a fair price and compare. The instinct to call a long price good value is the thing to unlearn first: value is a gap between two numbers, so a $1.40 favourite can be a value bet and a $9.00 outsider can be a terrible one.
The arithmetic is short enough to do in your head on a head to head, and it is the same arithmetic in every sport. What is specific to AFL is where the margin sits, how fast the prices move and how thin the edges are once you have taken the margin out.
A value bet in one calculation
Three steps. Turn each price into a chance, take the margin out, compare.
A decimal price implies a chance of 1 divided by the price, so $2.00 implies 50% and $4.00 implies 25%. Add the implied chances of every outcome in a market and the total comes to more than 100%: that excess is the bookmaker's margin, called the overround. Scale every chance down by the same factor until they add to 100% and you have a fair set of prices for that market.
Then edge = offered price / fair price - 1. Above zero is a value bet, below zero is you paying the margin.
Worked example: an AFL head to head
Illustrative prices, chosen to show the arithmetic rather than to describe a real game.
| Side | Priced at | Implies | Fair price |
|---|---|---|---|
| Home | $1.85 | 54.05% | $1.90 |
| Away | $2.05 | 48.78% | $2.11 |
The two implied chances add to 102.83%, so this market carries a 2.83% overround. Scaling both down by that factor gives the fair prices in the third column.
Now bring in the rest of the market. Say the best price anywhere on the home side is $1.92 and the best on the away side is still $2.05.
Example: home at $1.92 against a fair $1.90 is an edge of 0.92%. Away at $2.05 against a fair $2.11 is an edge of minus 2.76%. The same game, one bet and one donation.
That is the whole method. Everything after this is about making the fair price better and the edge survive contact with reality.
Why the market best price is usually still negative
This is the part that catches people out, and the arithmetic explains it in one line: a market best price has to beat the margin before it beats anything.
Take a line market quoted at $1.90 each way. Each side implies 52.63%, the book totals 105.26%, and both fair prices are $2.00. A best price of $1.97 on the favourite is still an edge of minus 1.50%, and $1.95 on the underdog is minus 2.50%. Shopping around improved the price and did not make it a bet.
So "I took the top price" is not a strategy on its own. The top price across the market is the starting point for the comparison, not the answer to it.
Where the margin sits in AFL markets
The overround is not spread evenly, and the arithmetic above gives you a way to measure it rather than guess.
- Head to head: the tightest market, usually a couple of per cent, because every operator prices it and the money concentrates there.
- Line and totals: a little wider, with the added problem that two operators can quote different lines, so the same bet is not on offer everywhere.
- Multi-outcome markets, margin bands, winning margin, first goalkicker: much wider, because the margin is divided across more outcomes and nobody notices a few per cent spread over twenty of them.
- Player markets: widest of all, and the most likely to be adjusted for a specific account.
Add up one over each price in any of these and the book total tells you what you are paying before you have an opinion about the game.
The de-vig choice, and what it does to your edge
Scaling every chance by the same factor is the simplest method and the one worth starting with. It also has a known flaw: it assumes the margin is spread evenly across the outcomes, and in practice bookmakers load more of it onto longshots.
That matters on AFL margin and first-scorer markets far more than on the head to head. On a two-way market at near-even prices the methods barely disagree. On a twenty-outcome market they disagree a lot, and even de-vigging will tell you a longshot is better value than it is. If your edges are all on the longest prices in a wide market, suspect the method before you believe the edge.
Sizing an edge that small
A 0.92% edge at $1.92 is a real edge and a tiny one, and the staking has to respect that. The Kelly stake is edge divided by the price minus one, as a share of bankroll, which here is about 1.00%. Most people use a fraction of that: a quarter Kelly on a $2,000 bankroll is about $5.
That figure is deliberately unimpressive, because it is the honest answer. Betting 5% of a bankroll into a 1% edge is not aggressive, it is a different activity. The reason to care about the arithmetic is that it converts an opinion about a game into a number you can size, and the number is usually small.
Risk: a bet above the fair price can lose, and at these edges a long losing run is ordinary rather than evidence of anything. There is no guarantee of profit, and the fair price is an estimate.
What to check before you trust an AFL edge
Five things, in the order they usually go wrong.
The price is stale. AFL markets move on team news and late outs, so a fair price built an hour ago may be describing a different game.
The line is not the same line. A bet at minus 15.5 is not comparable with one at minus 14.5, so a screen that mixes them manufactures an edge that is not there. AFL line betting covers how the settlement works.
The market is too wide. If the book totals 115% there is no fair price precise enough to find a 1% edge inside it.
The outcome is not what you think. Check how the operator settles a draw, an abandoned game and a late withdrawal, because an edge computed on one definition and settled on another is not an edge.
Your sample is too small to say anything. Measure closing line value, whether your price beat the market's last price, because it answers much sooner than profit does. See closing line value.
Where B337 fits
The +EV screener lists bookmaker prices that sit above the fair price and ranks them by edge, with the fair price built by taking the margin out of prices across the market and combining them. The de-vig is adjustable, so you can change which prices count and how much margin comes off each, and every edge is recalculated to match. Filter by sport, market and bookmaker.
Two honest limits. It is an estimate rather than a known probability, so a price above it can still lose. And B337 places no AFL bet by itself: the screener finds the price, and on Terminal Pro or Full Automation you place it into your own bookmaker accounts. A free account shows the live count of prices above fair and the best edge on the board, with the rows locked.
For the strategy around the markets themselves rather than the pricing, see AFL betting strategy, and for the method across every sport see value betting.