Time value of Money.
Net Present Value (NPV)
all equations are available only issue is what is the rate ?
In SL you may not get a constant value for 20 years due to constant change in our policies.
So take CB annual TB rate (not inflation rate) and calculate for each year with compound interest.(inflation is weighted average so to me it is not suitable to compare only a fixed sum of money. But if you generally talking it may be ok). By this way your opportunity cost for money will be discounted. So you can find out how much it cost today.(nor in real terms but statistically )
This is the only logical calculation if there is another let us know with reasons.
I am not a financial expert . They may come up with something different.
