From Opinion to Odds
Turn what you think into a price.
Theory: a price is a chance
Odds are a price for a chance. We use decimal odds: a winning £1 bet at 4.00 returns £4, your £1 back plus £3 profit. In fractional odds that's 3/1.
Every price also implies a chance: 1 divided by the odds. 4.00 implies 25%. That number is the break-even chance: the horse has to win more often than that for the bet to pay over time. At 2.00 you need better than 50%; at 5.00, better than 20%; at 15.00, better than about 6.7%.
Your opinion as percentages
To compare your view with the prices, you need it in numbers: a percentage for every horse, adding up to 100%. That's a probability line. The first one feels strange. Here is a simple way in:
- Rank the horses from your notes on level, conditions and readiness.
- Give the strongest their share first.
- Give every runner something. Outsiders do win.
- Adjust until the total is exactly 100%.
An invented five-runner race might come out like this:
| Horse | Your chance | Your fair odds |
|---|---|---|
| A | 35% | 2.86 |
| B | 25% | 4.00 |
| C | 20% | 5.00 |
| D | 12% | 8.33 |
| E | 8% | 12.50 |
Your fair odds are 1 divided by your chance.
Value
A bet has value when the price on offer is bigger than your fair odds. Say E is offered at 15.00. At your 8%, each £1 staked returns £1.20 on average (0.08 × 15.00). Say A is offered at 2.20. At your 35%, each £1 returns 77p on average (0.35 × 2.20). E is the better bet, even though A is far more likely to win.
That is the heart of this course: a good horse is not always a good bet, and the price decides.
Two warnings
Your percentages are opinions. Everyone's first lines are rough; the point is to make your view specific enough to check later.
And the bookmakers' odds include a margin. Add up 1 ÷ odds across a whole market and you get more than 100%. Small differences between your line and the market are usually not an edge, so look for gaps that are clearly big.
On a live card
On a live MWP card, the Handicapper panel turns your expected ratings into finishing distances in lengths, and the Pricing tool helps you build a line that adds up to 100%, with Guesstimate as a rough starting point. The historical cards in this course switch those tools off, so here you write the line yourself.
Practical: your first price line
Quiz: prices and chances
Up next: one race from start to finish, on your own.