The True Odds calc can be used to work out what a bookmakers odds for a market would be if their margin was removed. In other words, it shows what the bookie really thinks the odds should be.

This calc is particularly useful when we want to know the probability of an outcome but Betfair doesn’t have a market for it. It can also be used when Betfair does have a market but liquidity is poor.

The true odds can be used when calculating expected value, or just to get an idea of how big a margin the bookie is applying.

Using the Calc

This is a very easy calculator to use. If we want to work out the true odds of a market we just enter the bookie odds for each of the selections. Here is what it would look like for an NRL game between Penrith and Canberra:

The ‘Implied Probability’ is the percentage chance each team has of winning according to the bookie odds. However, you can see that these add up to a total probability of 104.84. In reality, it is impossible for these probabilities to be correct. The extra 4.84% is actually the bookies margin, or ‘Overround’.

To fix this, the calculator adjusts the probabilities so that we get the correct total of 100%. These probabilities are then converted to the true odds.

Adding Rows

If you are looking at a market with more than two potential outcomes you can add more rows by pressing the green button. You can add as many rows as you need.

Video Explainer