What is Net present value?
The value today of a stream of future cashflows, each discounted by how far away it is, less what you have to put in.
A positive figure means the project beats the rate you discounted at. It does not mean the project is a good idea, and the answer is only ever as good as the rate chosen.
NPV = sum of C_t / (1 + r)^tNot to be confused with Internal rate of return
NPV answers in money and IRR answers in percent, so IRR ignores scale. A tiny project with a spectacular percentage can be worth far less cash than a large one with a modest return, which is why NPV is the tie-breaker.