Shortening and drifting odds: what the move means for probability
Shortening odds are a price that falls, for example decimal 2.00 to 1.80, so the implied probability rises from 50.00% to 55.56%. Drifting odds are a price that rises, for example 2.00 to 2.20, so the implied probability falls to 45.45%.
Definition
Shortening means the odds on a selection get smaller. Drifting means they get bigger. In decimal form a move from 2.00 to 1.80 is shortening, and a move from 2.00 to 2.20 is drifting.
A shorter price means a higher implied probability, because you divide 1 by a smaller number. The method is set out in the guide on converting odds to implied probability.
| Move | Old probability | New probability | Change (percentage points) |
|---|---|---|---|
| 1.50 to 1.40 (shortens) | 66.67% | 71.43% | +4.76 |
| 2.00 to 1.80 (shortens) | 50.00% | 55.56% | +5.56 |
| 3.00 to 2.80 (shortens) | 33.33% | 35.71% | +2.38 |
| 1.50 to 1.60 (drifts) | 66.67% | 62.50% | −4.17 |
| 2.00 to 2.20 (drifts) | 50.00% | 45.45% | −4.55 |
| 3.00 to 3.20 (drifts) | 33.33% | 31.25% | −2.08 |
Illustrative example
A stake of KES 1,000 at 2.00 returns KES 2,000 if it wins. If the price then shortens to 1.80, the same stake would return KES 1,800 on a new bet, and 1 ÷ 1.80 = 0.5556, so the implied probability is 55.56%. If it drifts to 2.20 instead, a new KES 1,000 bet would return KES 2,200, and 1 ÷ 2.20 = 0.4545, or 45.45%.
Read the move with care
The same size of move changes the probability by different amounts at different prices, as the table shows. Both the old and the new percentage include the bookmaker's margin, so neither is a true chance; see calculating the bookmaker's margin. For where 2.00 sits against other prices, read odds-on and odds-against.
Regulation 23(1) of the Conduct of Gambling Operations Regulations, 2026 requires a licensee to clearly display betting odds, rules and terms, so the price and terms shown when you bet are the ones to read. A bet already placed keeps its accepted odds. Fractional prices follow the same logic, and decimal and fractional odds can be converted before comparing.
Safer-play note
A moving price is not a signal to stake more. Keep every stake inside the budget and limits you set beforehand. Gambling is addictive: play responsibly.
Questions and answers
Does shortening mean the selection is now more likely to win?
It means the implied probability of the price is higher. That figure includes the bookmaker's margin, so it is a reading of the price, not a measured chance.
Does a drifting price pay more if I already placed the bet?
No. A bet is settled at the odds accepted when it was placed. A later move changes only the price offered on new bets.
Is a shortening price a better price to take?
No. A shorter price pays less per shilling staked. Whether any price is worth taking depends on the true chance, which you cannot read from the price alone.