this is how I aim to split my $XX per hour rate charge:
* I pay myself a set amount - this less any tax due is my take-home (I will prob. be putting 25% of that in the business)
* I put about 60 cents (per hour) towards any phone bills (i.e. cell and broadband) - this will depend month-to-month depending whether how much top-up i use for my phone!
* About $1.60 (per hour) will go towards any computer equipment and new programs (yes, that's right, I'm thinking about getting a PC... but it won't be until mid-summer when I have finished taking leave as I won't be able to get to PC world til end of june :s)
* 46 cents (per hour) will be put aside for any incidentals (if there's none, then profit!)
Remember that I also have a JOB part time - that is why I will be doing my take-home at a Per hour rate
Don't forget that there is a calculator on this -
http://freelanceswitch.com/rates/ it is a great tool that you just fill in!