ands, using the buy/sell/buy-back prices in the original...

ands, using the buy/sell/buy-back prices in the original post:

Say you buy 100k @ 6.1c, it costs $6100 before brokerage.
You then sell 100k @ 7.4c, and receive $7400 proceeds.
That's $1300 gross profit before tax and brokerage.
At 30% marginal tax rate, the CGT payable is $390.
You now have $7010 net funds available, before brokerage.
BUT, to buy-back 100k @ 7.1c requires $7100, before brokerage.
SO, you've actually lost $90, plus whatever brokerage you've paid.

Of course, the assumption is that the shares have been held less than 12 months (hence, no 50% CGT concession), and a marginal tax rate of 30%.

For repeat trades of the same stock, I use the following formula to determine break-even buy-back price:

Buy-back price = 0.315*original buy price + 0.685*sell price.

This captures the 30% tax rate + 1.5% medicare levy.

If I don't believe the share price will drop substantially below the buy-back price in the short term, I don't sell. Hope that clarifies my line of thinking ;-)