Bundy, what araakan suggests is the set way.
What you're actually doing when you lay is taking odds on a horse will lose. (Usually).
Your bet is actually what you risk. The way to best maximise your return and control your risk of going broke is to regulate what you risk on each race. If you bet to win a set amount your risk (investment) will vary wildly from race to race.
What you should risk per race out of a $300 bank will depend on how aggressive you want to be. If the $300 was the entire amount you could risk and you were taking a long term view, I'd suggest you risk say 12% ($36) on each lay. You may want to be ale to lay the one's you think are massive unders for a bit more, say 16.7% ($50).
The other thing I'd say is don't be afraid to lay a winner. By this I mean if you lay horses that are unders but still well in the market, you are going to lay winners regularly. You are after a profit on turnover, and laying those shorter ones will give you good turnover with a more stable margin. if you only lay longer priced runners at big odds, your turnover will be low and one winner will have a bigger impact.
As you've started a specific thread, I'll attach the worksheet again here.
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