The 52.4% that decides everything

At −110 on both sides, a winning bet returns 1.909 for every 1 risked. Break-even is therefore 1 divided by 1.909, which is 52.38 per cent. Below that you lose money however right you feel; above it you make money however uncomfortable the run has been.

The number is not a convention anybody chose. It falls straight out of the margin: two sides of a coin flip priced at −110 each imply 52.4 per cent, and 52.4 plus 52.4 is 104.8. That extra 4.8 points of probability is the house's cut, and the break-even rate is simply what you must hit to give it back.

It moves with the price and only with the price. At −105 the threshold drops to 51.2 per cent; at −120 it rises to 54.5. A bettor who improves nothing about their selections and only their prices has changed the target they need to hit.

That is also the expensive part. Almost every advertised record sits within a point or two of a threshold the advertiser never prints. '54 per cent!' means nothing until you know what the average price was, and the price is the half that is always missing.

What to do with it. Work out the break-even rate for the prices you actually take, write it down, and compare your record to that number rather than to 50 per cent.

For any other price, the bet calculator gives the break-even percentage directly.