For a little over five years (I started in fall of 2008) I've been developing an app for the iPhone/iPad, and it's been for sale in the App Store for all of that time. I'm in a position now where I have an offer to sell the app to another party, including the App Store presence, all source code, and other assets. I'm tempted to take the offer since I could use the money in the sale right now, instead of the trickle of income the app generates each month (the offer price, minus commissions for the sale, would be a little over 13 months' worth of income from sales, if sales remain at the same pace).
My question is related to what taxes I might incur if I do decide to sell the intellectual property off. I haven't had much luck Googling for advice here, so really I'm just wondering what kind of income this would count as, and how it might be taxed. It is, after all, wholly a work of my own creation, from five years of off-and-on work. How would I value this work? Would income it generated over its lifetime contribute? Would I need to consider the amount of time I invested in development, along with salary ranges for a software engineer?