The time value of money. 100todayisworthmorethan100 in three years — you could invest today's $100 and earn interest, and inflation erodes future money's buying power. So future cash flows must be discounted back to their value in today's money before we compare them with a cost paid today.
Discount factors and present value. The exam gives you a table of discount factors (they depend on the chosen discount rate / cost of capital). The present value (PV) of a future cash flow is simply:
Present value = future net cash flow × discount factor
For example, 12,000receivedinoneyearata1010,908** — that future 12,000isworthonly10,908 in today's money.
Net present value (NPV) sums the present values of all the project's future net cash flows and subtracts the initial investment:
NPV = (sum of discounted cash flows) − initial investment
- Positive NPV → accept (the project adds value in today's money).
- Negative NPV → reject (it destroys value).
- When choosing between projects, the higher positive NPV is usually preferred.
Worked example (Project A, discount rate 10%):
| Year | Net cash flow ($) | Discount factor (10%) | Present value ($) |
|---|
| 1 | 60,000 | 0.909 | 54,540 |
| 2 | 70,000 | 0.826 | 57,820 |
| 3 | 80,000 | 0.751 | 60,080 |
| 4 | 60,000 | 0.683 | 40,980 |
| 5 | 40,000 | 0.621 | 24,840 |
| | Sum of PV | 238,260 |
NPV = 238,260 − 200,000 = +$38,260. The NPV is positive, so on this method the machine is worthwhile.
Advantages: the only method that accounts for the time value of money; uses all the cash flows over the whole life; gives a clear accept/reject signal in today's dollars.
Disadvantages: the most complex to calculate and explain; the result depends heavily on the discount rate chosen — pick the wrong rate and the decision can flip; still relies on uncertain forecast cash flows.