# What is a reduction factor?

When a horse is withdrawn from a race, the odds for all matched bets on the remaining horses are adjusted to account for the non-runner(s). This is because fewer horses in a race increase the probability of each remaining horse winning.

Reduction factors are similar to Tattersalls Committee Rule 4. This rule applies to all bookmakers and is calculated from the number of runners and the odds of the horse/s removed from the race.

'To win' market

Once calculated the reduction factor is applied by reducing the odds of any matched bets by the percentage of the reduction factor.

If you're using decimal odds, you can check this is correct using the following equation:

Old odds * ((100 - reduction factor) / 100) = New odds

'To place' market

Once calculated the reduction factor is applied by reducing the backer's potential winnings and the layer's potential loss of any matched bets by the percentage of the reduction factor.

If you're using decimal odds, you can check this is correct using the following equation:

For back bets: Old potential winnings * ((100 - reduction factor) / 100) = New potential winnings

For lay bets: Old liability * ((100-reduction factor) / 100) = New liability

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