What is meaning of Perpetuity
If annuity is expected to go on forever then it is known as a perpetuity and then the above formula reduces to:
Present value: A/i
Perpetuities aren't very common in financial decision making as no project is expected to last forever however there could be a few instances where returns are expected to be for a long indeterminable period. Particularly when calculating the cost of equity perpetuity concept is very useful.
For a growing perpetuity formula changes to:
Present value: A / i-g
All these calculations take into consideration that cash flow is coming at the end of the period.