Hmm ... my heads hurt doing math ... so not: e^(real x t) = e^(nominal x t) - e^(inflation x t) ? Like, you have 1$ in the bank that can buy 1 foo widget. A

Hmm ... my heads hurt doing math ... so not: e^(real x t) = e^(nominal x t) - e^(inflation x t) ? Like, you have 1$ in the bank that can buy 1 foo widget. After a year the foo widget is 1.65$ and you have 1.45$, missing 12% of the sum you need. I.e the same thing as having no inflation and a 12% tax. Your definition seem to break down when "nominal - inflation" is bigger than -100%. Or what would -110% real interest mean?