How to compare odds

[thebettrader]

Hello,

I was thinking and are not entirely sure when comparing odds against eachother. I will take an example and I am only looking for the mathematical formula not the true probability which I know is not the same. But if we assume that the below odds are the true probability for the example:

Moneyline:
Team1 odds: 1.54
Team2 odds: 2.72

Now I know that Team1 has the biggest chance of winning but what is the chance in % to win in this case for Team1?

Thank you!

[Nick JD]

Hello,

I was thinking and are not entirely sure when comparing odds against eachother. I will take an example and I am only looking for the mathematical formula not the true probability which I know is not the same. But if we assume that the below odds are the true probability for the example:

Moneyline:
Team1 odds: 1.54
Team2 odds: 2.72

Now I know that Team1 has the biggest chance of winning but what is the chance in % to win in this case for Team1?

Thank you!

1/decimal_odds * 100 = percentage chance of winning.

[thebettrader]

1/decimal_odds * 100 = percentage chance of winning.

Thanks, so that will then be:
1/1.54 * 100 = 64.934% chance of winning.

[Nick JD]

Thanks, so that will then be:
1/1.54 * 100 = 64.934% chance of winning.

Yup. Best way I found to get my head around it was the old coin toss (assuming also a "poor/silly" bookmaker offering zero over-round odds) such that heads and tails both offer decimal odds of 2.00

1/2.00 * 100 = 50% chance of heads I win, tails you lose.

It's also a very good way to understand the over-round: were I a bookmaker letting people bid on a coin toss I'd maybe offer 1.90 for both heads and tails:

1/1.90 * 100 = 52.6% x 2 "chance" of winning at these odds - which means as a bookmaker I would get 5.2% of the book remaining in my pocket every time I close the bets.

Or, you could offer a completely Fair betting system and charge a 5% commission. Either way - it's money for free after you pay the government their charge to legally remove money from people who struggle with mathematics!

[thebettrader]

Yup. Best way I found to get my head around it was the old coin toss (assuming also a "poor/silly" bookmaker offering zero over-round odds) such that heads and tails both offer decimal odds of 2.00

1/2.00 * 100 = 50% chance of heads I win, tails you lose.

Yes, that was a good way to remember how it is calculated.
The coin-toss example, I have red somewhere on the internet also and vig/margin that comes out for bookmakers when they lower the odds from its "true" probability as 1.9 vs 2.0.

In a way, perheps an exchange/betfair odds is more close to its actual true probability than a bookmakers odds is on average?

[Nick JD]

In a way, perheps an exchange/betfair odds is more close to its actual true probability than a bookmakers odds is on average?

That's an interesting question. Is BF's market book's over-round very close to 100% in the lead up to the off?

Should be, but probably isn't. There'd be an opportunity to profit if at any point it dips below 100%, so I'd guess bots would cover that side ... but maybe any over-round would exist as bouncing off 100% as it moves?

The fluctuation of prices about the "whole" 100% fascinates me. It's like they dance around swapping partners.

I wish my interest in this subject matched by understanding of it.

[thebettrader]

That's an interesting question. Is BF's market book's over-round very close to 100% in the lead up to the off?

but maybe any over-round would exist as bouncing off 100% as it moves?

The fluctuation of prices about the "whole" 100% fascinates me. It's like they dance around swapping partners.

I also wonder if the books are close to 100% before the off.

Yes, it is difficult to know exactly. I also wonder as you but I beleive as you say that the prices fluctuates around 100%. It seems to be like a balance around there but they should not move in exact sync at all times but will adjust quite quickly when it happens.
As you I try to understand this better

[jabe]

When you log into Betfair, you can see that the percentages are displayed on the market screen (the full one, not the displays with one price on each side).

It's Thursday and Liverpool play Villarreal this evening. In the Match Odds, the amount matched is £373,828. The back side adds up to 100.2% and the lay side 99.0%.

That is what you should expect for a "mature" market. The back side will be slightly over 100% and the lay side slightly below 100%.

This makes sense, otherwise you'd be able to back or lay all at current odds and make a profit. I've seen the figures at the "wrong" side of 100%, but only for a few moments.

When both sides of a market are close to the 100%, most runners (except, perhaps, outsiders) will have back and lay odds that are as close as they can be.


The opposite situation arises with events that are not as popular.

There is a game this evening between CA Collegiales (Res) and CA All Boys (Res) in Argentina. It's a reserves game. and it starts in less than six hours.

The correct score percentages are 1850.5% and 0%. Nothing has been matched, and you can back all but two runners at 1.03 for £2 or 1.02 for £52. There are no amounts waiting on the lay side. I'm sure there are bots placing these low-price back bets in all markets. My belief, which may be wrong, is that they are hoping to catch out people who make a mistake placing their bets.

The game's match odds have had a little action - a massive £11 has already been matched and there are three or more odds awaiting on the back and lay sides, though there are still big gaps between each side. The percentages are 112.1% and 75.3%.


If you intend to trade on a market, it makes sense to choose a mature market. When a certain amount has been matched or when the percentages are close (you decide how close) to 100% seem to be suitable indicators.

[thebettrader]

When both sides of a market are close to the 100%, most runners (except, perhaps, outsiders) will have back and lay odds that are as close as they can be.

Yes it is a good thing to check for that a market is mature, where the lay side also is below.
When big gaps between lay and back odds, that doesn't either feel so right and "mature" yet.
I have also seen bets been placed on very low odds like 1.03 very often.

As you say, I also thought it could be bots placing them hoping for anyone to do a mistake somewhere. It is a theory or it is wrong.