Based on your financial expertise, provide your response or viewpoint on the given financial question or topic. The response format is open.

What is the equation for an inflation adjusted annuity held in perpetuity?
The question lacks specificity, i.e. when does the initial investment occur, now or one period from now?  If now then it is a perpetuity due.   I  will consider under 2 scenarios, A and B, relating to the size of the initial investment. A. Assuming that the initial investment (C_0) occurs now and each payment thereafter has the relationship (1+g) with this investment then the relevant base equation is that for the present value of a growing perpetuity due, expressed in terms of C_0, i.e.  PVGPD=  [C_0*(1+g)*(1+i)]/(i-g). Now, to suit the question asked, we can see that i=fixed rate of return (f) and g = expected inflation rate (e) such that we can rewrite the equation as PVGPD = [C_0*(1+e)*(1+i)]/(i-e].   We know that f = is a fixed nominal rate and must be adjusted for e to calculate the real rate (r) according to the equation f=(1+r)*(1+e)-1. Therefore  PVGPD = [C_0*(1+e)(1+(1+r)(1+e)-1)]/((1+r)*(1+e)-1-e] Tidying up  PVGPD = {C_0*(1+r)(1+e)^2}/[r(1+e)] PVGPD = [C_0*(1+r)*(1+e)]/r B. Assuming that the initial investment (X) is not equal to each subsequent perpetual payment (C_1) then the relevant base equation is that for the the initial investment plus the present value of a growing perpetuity, i.e.  PVGP=  X + [C_1/(i-g)] Rewriting  PVGP = X + [C_1/(f-e)]    Substituting PVGPD = X + {C_1/[(1+r)*(1+e)-1-e]} Tidying up  PVGPD = X + C_1/[r*(1+e)]