Lsbcal
Give me a museum and I'll fill it. (Picasso) Give me a forum ...
I think you are thinking of bond nominal returns, before inflation. If bonds return 4% but inflation was 8% the real return is -4%. And this doesn't even take into account taxes which will eventually have to be paid even if your bonds are in a retirement account.From 1970-2007, I have yet to find a year where both the S&P 500 lost and so did bonds. 1994 was close (bonds negative, S&P500 positive), and so was 1973 (bonds positive, S&P500 really negative). The current economic environment is far closer to 1973-74 than 1994. A repeat of 1973-74 would be brutal.
FIRECalc specifically takes inflation into account. If we had deflation you could have small negative nominal returns in stocks and bonds but because your purchasing power went up it's possible that the FIRECalc numbers will actually increase -- take a look at the early 1930's.