AFL Betting: Working Out the Margin on a Line Before You Take It

An AFL line market looks like a coin flip with a handicap attached, and the handicap is not where the cost is. The cost is in the pair of prices, it is calculable in about ten seconds, and it is the only number that applies to every bet you will ever place on the code. This page shows the calculation and the settlement clauses that decide the rest.

The margin is in the pair of prices, not the handicap

A line market sets a handicap intended to make both sides close to even money, then prices both sides below even money. That gap is the operator's margin. The handicap itself is an opinion about the match and costs you nothing directly; the pricing is a fee you pay on every bet, win or lose. Separating the two is the whole skill of reading a line market as a money proposition rather than a football one.

How to calculate it

Convert each price to an implied probability by dividing one by the decimal odds, then add the two together. A fair two-way market totals one. Two sides at one dollar ninety give about zero point five two six each, totalling roughly one point zero five three — a margin of about five per cent. Two sides at one dollar ninety-five total about one point zero two six, roughly two and a half per cent. The second market costs you half as much to bet into for exactly the same bet.

Why it matters more than any single result

Over one bet, margin is noise. Over a season of weekly bets it is the dominant term: a punter staking two hundred dollars a week into five per cent markets is paying about ten dollars a week in margin, which is around two hundred and twenty dollars across a full home-and-away season before a single result is considered. Halving the margin halves that figure, and nothing about your tipping has to improve.

Totals markets use the same arithmetic

An over-under on total points works identically: a number chosen to sit near the middle of the expected distribution, with both sides priced under even money. Add the two implied probabilities and you have the margin. The only extra thing to check is what happens if the total lands exactly on the posted number, because that outcome is handled by the operator's own rules rather than by arithmetic.

• Add both sides of every two-way market before taking either.
• Check the rule for an exact landing on the line or the total.
• Compare the same market at the same time; prices move.
• A half-point line removes the exact-landing case entirely.

Multis compound the margin you already paid

A multi multiplies the odds of each leg together, and it multiplies the margin along with them. If each leg carries five per cent, a four-leg multi carries roughly one point zero five to the fourth power — about twenty-two per cent over fair. The payout looks enormous because the odds compound. The cost compounds at exactly the same rate, and it is the cost that decides your long-run result.

The worked compounding

Two legs at five per cent each give about ten and a quarter per cent. Three legs give about sixteen. Four legs give about twenty-two. Six legs give about thirty-four. None of this requires the legs to be badly chosen — it is pure arithmetic on the margin, and it applies to a multi of four favourites just as much as to a long shot.

1. Calculate the margin on each leg separately.
2. Multiply the margins, do not add them.
3. Compare the result with the margin on a single bet of the same stake.
4. For a same-game multi, accept that correlation is priced by the operator and the margin cannot be decomposed from outside.

Same game multis are a different object

When legs come from one match they are correlated, so the operator does not simply multiply the prices — it models the joint outcome and prices that. From outside, you cannot separate the correlation adjustment from the margin, which means you cannot calculate what the market costs. That is not a claim that it is unfair; it is a statement that the one check available to you on an ordinary market is unavailable here.

What a bonus bet on a line is actually worth

The common form of promotional credit does not return the stake with a win. On a line market priced at one dollar ninety, a fifty dollar bonus bet therefore returns forty-five dollars of winnings, not ninety-five, because the fifty is kept. Its real value is the stake multiplied by the odds minus one — and on short odds that is a long way below face value.

The arithmetic across odds

At one dollar ninety a fifty dollar bonus bet is worth forty-five dollars of upside. At three dollars it is worth a hundred. At one dollar twenty it is worth ten. Promotions commonly set a minimum odds condition precisely because the value is so sensitive to that number, so read the minimum odds and calculate the value at that minimum rather than at the odds you hope to find.

• Value of a stake-not-returned bonus bet = stake x (odds - 1).
• Check the minimum odds condition and the excluded markets.
• Check whether cashing out voids the promotion entirely.
• Check what happens if the event is postponed or the market is voided.

Settlement clauses decide the awkward cases

Football produces a steady supply of outcomes that arithmetic does not cover: a drawn match on a head-to-head market, a total landing exactly on the posted number, a match abandoned at half time, a fixture moved to another ground or another date. Every one of those is resolved by the operator's published rules, not by convention, and the rules differ between operators.

The four clauses worth reading once

What happens to a head-to-head if the scores are level; what happens to a line or total that lands exactly; what happens to a market if the match is abandoned before or after a stated point; and what happens if the venue or date changes. Reading those four once, for the operator you use, covers almost every dispute that arises in a season and takes about five minutes.

• Level scores on a head-to-head: refunded, settled as a dead heat, or a separate draw price.
• Exact landing: refunded, or impossible if the line carries a half point.
• Abandonment: void, or settled on the score at the time, depending on the rule.
• Venue or date change: markets may stand or be voided; the rule says which.

Where to read on

Each of these covers one part of the same arithmetic in more detail, so you can check a figure rather than take it on trust.

Read next

• Multis and cash-out arithmetic
• Odds, margin and staking
• Promotion terms, priced
• Line betting
• Totals markets
• Same game multis

The small print that actually matters

18+ and where to get help

Everything on this page is information about how money moves, not advice to gamble and not a promise that any bet or spin returns anything. Wagering is for adults over 18 only. If the amounts, the chasing or the hours have stopped feeling like a choice, Gambling Help Online is free, confidential and open at any hour on 1800 858 858, and BetStop is the national self-exclusion register for licensed Australian wagering operators — it does not reach offshore online casinos, which is one more reason to decide the limit before the deposit rather than after it.