How to calculate total spent and payout and estimating if exchange wins correctly using excel.
500 at 7 odds gives me $3500 [Bookmaker]
Lay at 933.33 at 3.8 gives me $3546.6667 [Exchange]
With a liability of 2613

Total spent is 3113
So if bookmaker wins:
Total spent
3500 (payout) – 3113 (total spent)
= 387
If bookmaker wins

Exchange
Payout – total spent gives me
3546 - 3113
= 433 [Incorrect value].
How do I incorporate the 5% commission as this seems very incorrect.

[Exchange]
The payout is lay bet * lay odds
And the lay bet was calculiated by Lay amount = (Back stake*Back odds*back commission) / (Lay odds – Lay commission)

Any ideas why it’s doing this?