HI,

I don't think there will be a simple formula. You will have to do it by iteration and if you are taking the bets you won't be able to guarantee your position unless you decide on the amount of the next bet. Briefly, your spreadsheet will have columns for the Horse ID; Total Staked (on each horse); Amount to be paid if horse wins (excluding the stake); Existing Odds (the Total Payments liable divided by the amount staked); Future Bet; Future Target Winnings.

The odds for the first bet on each horse will be an intelligent guess (if 8 horses, give each horse odds of 8-1 unless you want to allow for favourites.)

Thereafter you can calculate the effect of an additional, say, £5. bet on each horse and adjust the odds on each horse to reflect that effect. As far as I know it is not an exact science and is done by iteration. Perhaps someone else knows differently. If you were very good at maths, then I suspect that you could use the process called Integration, which is a complicated way to do iteration.

Before I can go any further, I would need tha answers to my previous post.