If a bookie is running a promo that pays out if at least one out of two, or more, selections wins, you can use the combined odds calc to work out whether that promo is +EV.

For example…

The above promo would pay out at $3 odds if either Behemoth or Gytrash won their race (The Goodwood at Morphettville, 15/5/21). The respective starting prices for those horses were $4.60 and $2.70.

We can use the calculator to see just how much value was in the promo.

Based on the starting prices, there was a 58.78% probability that one of those two horses would win. This translates to fair odds of $1.70.

Therefore, the promo odds of $3 definitely had a positive expected value and were worth taking.

If the bookie had included a third horse in the promo we could just have clicked on ‘Add More Selections’ to add an extra row to the calc.