NPV demonstrates the expected return on investment, which
is a great way to justify your marketing budget. I use your sales funnel to
calculate the probability-adjusted value of your customers, then decide a
discount (risk) factor and work out how much it'd be if a proposed marketing
programme hit its goals. The basic rule: if NPV>0, the
project is worth doing.
The basis of NPV is that a pound in your pocket today is worth more than a
pound promised to you next year; the risk of not delivering that promise reduces
the present value of that future pound. NPV calculus lets
you work out how much an increase in value (i.e. a growth in sales) tomorrow
is worth today, letting you put costs and ROI into your marketing plan.