In: Economics
An Individual lives for two periods, 1 and 2. In the first he works and earn an income of M. In the second he is retired and has no income.
His/her life time utility is a function of how much he consumes in the two periods. C1 denotes consumption in period 1 and C2 consumption in period 2. (Hint: If you want to, you can view and treat C1 and C2 as any pair of “goods”, e.g. good x and y).
He/her uses one part of M to buy C1 in period 1 and saves the rest to buy C2 in period 2.
This means that C1=M-S, where S denotes how much the individual saves of his earnings M.
The price of both C1 and C2 is equal to 1.
The amount he saves earns an interest rate of r implying that C2=(1+r)S
The individuals budget restriction could for instance hence be written as:
M = C1+S or M=C1+C2/(1+r).
Now, the individual has an utility function U=lnC1+(1-d)lnC2 where 0<d<1. The term d denotes a discount factor, i.e. that the individual values consumption in period 2 lower than consumption in period 1.