Lay bet calculator: liability and profit after commission

Lay bet calculator

Backer's stake: -
Your liability: -
If the selection loses: -
If the selection wins: -

Key facts

Liability = backer's stake x (lay odds - 1). Laying $50 at $5.00 risks $200 to win $50.
Exchange commission comes off your net winnings. At Betfair's usual 8% on Australian racing, that $50 win becomes $46.
In our calculation a lay at $5.00 with 8% commission only breaks even if the selection's true chance of winning is 18.70%, not the 20% the price implies.
The longer the lay odds, the more you risk for the same win: at $21.00 you put $1,000 on the line to win $46.

How to use the lay bet calculator

Choose whether you know the backer's stake (the amount you want to win) or the liability you are willing to risk, enter that amount, the lay odds and the commission rate. The calculator shows both figures, your profit if the selection loses, your loss if it wins, and the true chance at which the lay breaks even. Betfair's guide describes the backer's stake as the money you want to profit from, so most punters start there; switch to liability when you want to cap what you can lose.

What a lay bet is

A lay bet is a bet that something will not happen. Betfair's own guide puts it simply: "When you place a lay bet, you are betting on something not to happen." Lay a horse and you win if any other runner wins the race. Lay a team and you win if it loses or, in markets with a draw, if it draws.

You can only lay on a betting exchange, because there you take the bookmaker's side of someone else's back bet. A normal bookmaker sells you only the back side. If you are new to exchanges, our guide to the betting exchange in Australia explains how the market works, and lay betting covers the strategies people use.

The lay bet formula

Three lines cover every lay bet:

Liability = backer's stake x (lay odds - 1). This is Betfair's own formula, written as lay odds times backer's stake, minus backer's stake.
Profit if the selection loses = backer's stake x (1 - commission).
Loss if the selection wins = liability. Commission is taken from net winnings, so a losing lay pays no commission.

To lay to a fixed liability, turn the first line around: backer's stake = liability / (lay odds - 1). Risking $100 at $5.00 lets you lay a $25 backer's stake.

Worked example: laying a $5.00 runner

You think a horse is over-rated at $5.00 and lay a $50 backer's stake on an Australian racing market. Betfair says its base commission on Australian racing is usually 8%.

Liability: $50 x (5.00 - 1) = $200. This is the most you can lose on the bet.
If the horse loses: you win the $50 stake, less 8% commission ($4.00), so +$46.00.
If the horse wins: you pay the backer's $200 profit, so -$200.00.
Break-even: you need $46 x (1 - p) = $200 x p, which gives p = 18.70% in our calculation.

The price of $5.00 implies a 20% chance. Commission moves your target to 18.70%: rate the horse at 15% and the lay is worth +$9.10 on average, rate it at 20% and it is worth -$3.20. Laying at the fair price is still a losing bet once commission is paid. Our implied probability calculator turns any price into the chance it implies.

How liability grows with the lay odds

The same $50 backer's stake looks very different at different prices. In our calculation, with 8% and 6% commission:

Lay odds	Liability	Profit if it loses (8%)	Implied chance	Break-even at 8%	Break-even at 6%
$1.50	$25	$46.00	66.67%	64.79%	65.28%
$2.00	$50	$46.00	50.00%	47.92%	48.45%
$3.00	$100	$46.00	33.33%	31.51%	31.97%
$5.00	$200	$46.00	20.00%	18.70%	19.03%
$8.00	$350	$46.00	12.50%	11.62%	11.84%
$11.00	$500	$46.00	9.09%	8.42%	8.59%
$21.00	$1,000	$46.00	4.76%	4.40%	4.49%

Two things stand out. Your win is capped at the backer's stake, while your risk rises with every tick of the price. And commission costs you a bigger share of the implied chance on short-priced lays: at $1.50 the gap between 66.67% and 64.79% is almost 2 points.

Pundit tip: decide on your liability first, then convert it to a backer's stake. Laying a "sure loser" at a long price is how a $50 bet turns into a $1,000 loss.

Commission rates to enter

Betfair's guide says commission is taken "from a customer's net winnings" at a Market Base Rate. On Australian racing that is usually 8%, with 6% in some states, New Zealand and international racing and 10% in others. Sports markets are 6%, except NRL markets at 10%.

Lay betting with a back bet

Most punters lay to offset a back bet, not on its own. Back a runner with a bookmaker and lay it on the exchange, and the two bets cancel out, leaving a small locked result either way. That is the basis of matched betting in Australia. For an exact lay stake against a back bet, use our hedge bet calculator, which works out the stake that gives the same profit on both outcomes.

Rules in Australia

Betfair Pty Limited says it is licensed and regulated by the Northern Territory Government. The usual national rules apply: ACMA says in-play betting on sports matches online is prohibited, with a phone exception only where the whole bet is made "wholly via the phone call", and you cannot fund a betting account with a credit card or crypto. Laying is still gambling with real liability, so set limits before you start, and if it is getting out of hand, free and confidential help is a phone call away.

Frequently asked questions

How do you calculate lay liability?

Multiply the backer's stake by the lay odds minus 1. Laying a $50 backer's stake at $5.00 gives a liability of $50 x 4 = $200, which is what you pay if the selection wins.

What do I win on a lay bet?

If the selection loses, you win the backer's stake, less the exchange's commission on your net winnings. A $50 lay with 8% commission returns $46 profit.

What is the difference between backer's stake and liability?

The backer's stake is what you win if the selection loses. Your liability is what you lose if it wins. They are only equal at lay odds of $2.00; above that, your liability is bigger than what you can win.

Can I lay bets with an Australian bookmaker?

No, a standard bookmaker only lets you back. Laying needs a betting exchange, where another punter takes the other side. Betfair Pty Limited says it is licensed and regulated by the Northern Territory Government.

Is laying the favourite a good strategy?

Only when you rate its chance below the break-even figure the calculator shows. A short-priced lay risks less per bet, but you still lose whenever the favourite wins, and commission comes off every winning lay.