The article explores how public funding is different from private financing and how this affects social discounting. It shows that the cost of risk in public benefits decreases in value, not rate of return. Some governments may use a 'social opportunity cost' discounting method, while others may need lower rates. A hybrid regime can handle this. It also suggests that optimizing spending from constrained budgets is better than using a shadow price for public spending. The study looks at US Federal and UK government practices, showing the challenges of implementing social discounting in real-world situations.