Once again, we've learned that there are people (not very many) who live on "rents" - income from the ownership of assets such as land, buildings, stocks, bonds, mineral rights, etc. This income is known to most of us as "mailbox money" because we really like the idea of checks that arrive at our homes without the inconvenience of leaving them to earn the money. [...] this year, for the second in a row, I can proudly announce that the cost of being independently upper-middle class has declined. The combination of modest inflation and an uptick in fixed-income yields has reduced the amount of assets you need to be a full-time mailbox money person to only $4,184,483. The basis for this figure is my Life of Riley Index, an effort to track the cost of being a person of independent means at a level of income that is comfortable, but not conspicuous. [...] as a careful and conservative rentier, we ask how much you would need in investments to produce that $74,449 at current yields. [...] noting that many financial planners have identified a 4 percent annual withdrawal rate as "safe," we do the calculation again. [...] we do the figure for retirees by assuming that Social Security and/or a pension will provide 40 percent of the required income.