Sheeds over at Windows Phone Down Under has developed a Windows Phone Return on Investment calculator to help developers on the financial end of app development. The calculator is used to estimate app revenue streams, for paid apps, based on a number of variables.
In a nutshell, the calculator takes into account your development costs, taxes and Microsoft's cut. Then based on different price points and monthly sales projections it will show you how many months it will take for you to break even. According to the calculator's description,
"The calculator is an Australian tool to help calculate U.S. and Australian taxes, Microsoft's revenue share and local developer costs to develop (time and money) in order to help the Windows Phone developer determine profitability and return on investment (breakeven) for various scenarios."
Naturally, there is a disclaimer to all this. The calculator is used to estimate your returns and there is no guarantee your monthly sales will match the projections used in the calculator. Still, it looks like a nice tool to bring the financial end of app development into focus.
You can download the Windows Phone 7 ROI Calculator here.