Margin of safety is Benjamin Graham's core idea. Intrinsic value is an estimate, not a measurement, and you can be wrong about it. The margin of safety is the cushion between today's price and your value estimate, wide enough that even a sizable error still leaves you with a good price.
How to read it: • 30% or more: the textbook "buy with a buffer" zone, with plenty of room for error in the value estimate • 0% to 30%: fair to cheap, but no real cushion if the value estimate is wrong • Between negative 10% and 0%: a slight premium, ordinary market territory • Negative 10% or worse: paying a real premium to your value estimate. Either you trust the future more than the estimate captures, or the position needs a hard look.
The 30% level is a convention, not a law. Graham himself used 50% on smaller, cheaper situations, and Buffett accepts thinner margins on businesses he knows extremely well. The plain version: the bigger the margin, the more wrong you can be and still be safe.
This is figured against each value estimate on its own, such as EPV and the DCF base case, so the spread of margins across the different methods is the real signal. When all the methods agree at 30% or more, that is the rare clear-cut case. Disagreement is the usual one.