OK. But by that calculation everything else returns much less. Many potential investments (CDs, bank accounts, many US government bonds) have negative returns.

OK. But by that calculation everything else returns much less. Many potential investments (CDs, bank accounts, many US government bonds) have negative returns. This is an all-in calculation, in which you get 4% on your money absolutely free and with zero risk (because all of the costs, risks, and even inflation are accounted for in the calculation). Put a dollar in today, and 18 years from now you'll have $2 to do with as you will, at today's prices. Presenting the number as 4% only sounds low when you compare it to numbers calculated on a different basis.