Margin of safety

Every valuation is an estimate built on assumptions that will be partly wrong. The margin of safety is the discipline that protects you from those errors: buy only when the price is well below your estimate of value, so a mistake in your assumptions still leaves you whole.

The idea

The concept comes from value investing: never pay full estimated value, because your estimate could be too high. The gap between price and value is your buffer.

Margin of safety = (Value - Price) / Value

A worked example

Your DCF and multiples agree the business is worth about 15.00 per share. The market offers it at 10.50:

Margin of safety = (15.00 - 10.50) / 15.00 = 30%

A 30% cushion means your value estimate could be 30% too optimistic and you would still merely break even — anything better is profit. Many disciplined investors demand a 25-50% margin before buying.

Why it works

• It absorbs estimation error — bad inputs, an over-rosy forecast.
• It absorbs bad luck — a recession, a missed quarter.
• It improves the odds: a wider gap between price and value means more ways to win and fewer to lose.

The margin of safety converts valuation from a precise-looking but fragile number into a robust decision rule. The next lesson covers the errors it is most often protecting you from.