It must be much higher than the 4% a typical American in your position has left. I'd be curious what the best case real world numbers are for people in your situation who are doing their best to optimize.

Which was on response to:

Personal anecdote: My own finances as well as those of six of my friends fall well outside those bands. (Emphasis added.)

You still seem to be missing the point. Statistical averages, even in percentage form, cannot be blindly projected across the entire income scale. Someone making $1M a year does not spend the same percentage on food as someone making $40k.

And what does it matter if he takes money out of his housing budget and directs it towards an expensive car? The point of disposable income is that you get to spend it on things you want. That includes nicer housing, restaurant meals, and fancy cars, the value of which is ignored in your calculations.

I track my finances directly in a CoffeeScript source code file and use a simple home-brewed software library to compute my net liquid assets and (when necessary) my estimated tax payments and projected tax liabilities. You've reminded me that I really should be using something like Quicken for finer-grained analysis, so I'll look into that and post my numbers later this week (edit: one second thought, it doesn't seem worth the extra friction).

My living costs followed a general upward trend that leveled off in late 2009, but my salary data is extremely messy for several reasons:

• I had no grasp of what I was worth until 2007.
• I had no interest in anything beyond emergency savings until mid 2009, and preferred to gamble on startup equity being worth something, reasoning that I was in my twenties and had plenty of time to settle down later.
• I was too personally attached to the startup I worked at until early 2010.

It's hard to imagine changing my past since it'd mean giving up several of my current friendships, but the decisions I made in reality were emphatically the wrong ones from a financial perspective: I worked at-cost for six years and left several hundred thousand dollars of potential salary on the table.

(At-cost was both the mode and the mean, but some months were significantly higher and some were unpaid.)

Here's what I've realized in the last two years:

• Startups are harder and more stressful than normal jobs, and as you get closer to founder-level the effect intensifies.
• I can get a competitive salary even if I choose to work for a startup.
• Savings can be used to fund my personal projects which:
  • are more fun than work;
  • might generate revenue;
  • could seed a startup of my own;
  • will hopefully improve the world.
• Savings can also be used to vote for causes I think will improve the world.
• There are risks: The labor market for software engineers may cool off, my costs may spike if I decide to start a family or have medical problems, and I may choose or be forced to retire.

I'm still determining the split between my own projects, other causes, and risk management, but my personal projects decisively dominate any significant increases in my personal consumption, which is why I don't exhibit income elasticity for housing, why I use public transit instead of owning a car, and why I don't eat out very frequently.