[teraflop]

> The reason being that, over a 5+ year investment horizon, a total US market portfolio will average about 6% after inflation.

Leaving aside the issue that past performance does not guarantee future performance:

If you're talking about "averages" based on historical data, then the average annual return over a 5-year period is -- by definition -- the same as the average return per year. The investment horizon doesn't affect the average expected return, but it does affect the dispersion of outcomes around that average.

I think it's a bit irresponsible to say that a 5-year investment "will average" 6%, when the standard deviation of that number is something like 8-10%. Seeing negative real returns over 5 year periods isn't just a theoretical possibility; it's historically fairly common.