# What is a fair odds line, and how do you make one?

When betting on horse races, picking the right horse is only half the equation. Since it’s basically impossible to pick 100% winners, betting when the odds are suitable is a key to long-term success.

But how do you determine when the odds warrant a bet? That’s where a fair odds line comes into play.

### What is a fair odds line?

A fair odds line is equal parts a handicapping challenge and a math exercise. Let’s say you’re handicapping an eight-horse field, and you’ve analyzed all the contenders to determine their likelihood of winning.

Now it’s time to turn your opinions into numbers. Let’s say you believe Horse #1 has a 20% chance of winning. That means if the race were run five times, you would expect Horse #1 to lose four times and win once. Four to one… 4-1!

It’s really that simple. Horse #1 is a fair win bet at odds of 4-1 or higher. If Horse #1 starts below 4-1, his odds no longer reflect his likelihood of winning according to your handicapping. Assuming your percentages are correct (and that’s the tricky part!), you shouldn’t bet Horse #1 to win at less than 4-1.

### How to create a fair odds line

The key to creating a fair odds line is making sure all the percentages add up to 100%. You can’t assign every horse in an eight-horse field a 20% chance of winning, because then their combined chances would add up to 160%, which is a mathematical impossibility.

Per the 2009 American Racing Manual published by Daily Racing Form Press, common odds translate to perceived win percentages as follows:

OddsWin chanceOddsWin chance
 1-20 95.2 6-1 14.29 1-10 90.91 7-1 12.5 1-5 83.33 8-1 11.11 1-4 80 9-1 10 3-10 76.92 10-1 9.09 2-5 71.42 11-1 8.33 1-2 66.67 12-1 7.69 3-5 62.5 13-1 7.14 7-10 58.84 14-1 6.66 4-5 55.55 15-1 6.25 9-10 52.63 16-1 5.88 1-1 50 17-1 5.55 6-5 45.45 18-1 5.26 7-5 41.67 19-1 5 8-5 38.46 20-1 4.76 9-5 35.71 25-1 3.85 2-1 33.33 30-1 3.23 5-2 28.57 40-1 2.44 3-1 25 50-1 1.96 7-2 22.23 60-1 1.64 4-1 20 75-1 1.32 9-2 18.19 80-1 1.24 5-1 16.67 100-1 0.99

Therefore, a fair odds line for an eight-horse field might look something like this:

Horse #Win chanceFair odds
 #1 33.33% 5-2 #2 20.00% 4-1 #3 11.11% 8-1 #4 2.44% 40-1 #5 14.29% 6-1 #6 4.76% 20-1 #7 9.09% 10-1 #8 4.76% 20-1

The percentages listed above add up to 99.78%; you don’t have to worry about getting to exactly 100%.

After compiling your fair odds line, you can compare your fair odds with the actual odds as post time approaches. If Horse #1 is listed at 7-2, congratulations—you’ve found more-than-fair betting value! On the other hand, if Horse #1 is listed at 8-5, perhaps you should consider betting Horse #2 if the available odds are higher than your 4-1 fair odds.

One side note—be careful not to overemphasize perceived value where high odds are concerned. It’s tempting to think a horse listed at 30-1 on your fair odds line is great value if he’s 50-1 in the actual betting, but we’re talking about the difference between a 3.23% chance of winning and a 1.96% chance of winning. It's hard to accurately split the percentages so finely, especially on a horse you believe has a very small chance at winning.

Now that you’re up to speed on calculating fair odds, you’re better equipped to play horses whose odds reflect their chances of winning according to your handicapping. Good luck!