A popular mechanism of quantifying the Present Value of the future Cash Flow \mbox{CF}:


where
T  total number of accounting periods 

i= 0, 1, 2, 3, ...  running number of accounting period (usually 1 year) 
r  discount rate 
\mbox{CF}_i  Cash Flow generated during the ith accounting period 
\mbox{DCF}_i  discounted value of Cash Flow generated during the ith accounting period 
\mbox{DCF}  discounted value of total cash generated over "n" accounting periods 
\mbox{PV}_r[CF]  Present Value of future cash flows \mbox{CF} at discount rate r 
The main idea of DCF is that value of cash today is deemed by the majority of cash owners as higher than value of future cash because it is already in hand and it can be spent by owner or can be invested in readily available lowrisk investment market opportunities and assure a certain profit. While future cash may not happen at all or may be lower than returns from readily available lowrisk investment.
The corresponding discount of the cash value over time is controlled by Discount Rate (usually denoted as
r) which is normally set along with Weighted Average Cost of Capital (WACC).
Investor normally would like to compare different investment opportunities and give early returns more weight and as such comparing DCF rather than FCF.
DCF is used to calculate Net Present Value (NPV) to prioritise investment projects.
See also
Economics / Money / Currency / Cash / Cash Flow
[ Investment / Financial Investment / Cash Discount ]
[ Present Value (PV)][ Profitability Index (PI) ] [ Net Present Value (NPV) ] [ Internal Rate of Return (IRR) ]