The Net Present Value (NPV) Rule is a financial tool used to determine the value of potential investments. Investors use the NPV Rule to determine whether a specific project or investment is likely to yield a positive return before they commit to the undertaking. It is a commonly used method used in the financial world to assess whether an investment opportunity is likely to make a desirable return in the short or long-term future.

The concept of the Net Present Value Rule is based on the idea that money received and spent at different times is worth different amounts. In general, money today is worth more than money received in the future. The difference in value is due to the concept of the time value of money which states that a given amount of money will be worth more if it is received today than if it is received at a later date due to the potential to be invested and generate returns.

To calculate the NPV of an investment opportunity, the investor must calculate the present value of all cash inflows and outflows associated with the project. The NPV Rule uses a discount rate to account for the time value of money, this rate is typically the investor's required rate of return. The investor's required rate of return reflects the amount of return they require to make an investment profitable. All cash inflows are added together and all outflows are subtracted. If the net present value (NPV) of the investment is positive, then it is likely to be a good investment opportunity with a desirable return. However, if the NPV is negative, the investment is considered to have a lower return than is required, and the investor should avoid making the investment.

The NPV Rule is an important tool used by many corporate and individual investors to determine whether an investment is likely to yield a positive return, and should be considered as part of any investor's strategy when considering a new opportunity. This tool can provide valuable insight into the expected returns of a given project and, if used correctly, can help investors manage their risks and ensure that viable investments are identified.