Margin of Safety Explained: How Big a Discount You Need

Margin of safety is the gap between a stock's estimated intrinsic value and the price you pay, expressed as a percentage. It is the cushion that protects you when your valuation proves too optimistic. Benjamin Graham, who coined the term, often looked to buy at no more than two-thirds of intrinsic value, a margin of safety of about a third.

The formula

Margin of safety equals intrinsic value minus price, divided by intrinsic value. Multiply by 100 for a percentage. The bigger the number, the more room you have to be wrong and still avoid a permanent loss. The arithmetic is deliberately simple, but its value lies in forcing you to commit to an explicit estimate of worth before you act, rather than reacting to the price alone.

Worked example. You estimate a stock's intrinsic value at $100 and the market offers it at $70. Margin of safety = (100 − 70) ÷ 100 = 30%. If your valuation was 20% too optimistic, the real value is $80, you still paid below it. The discount did its job: it absorbed your error and left you with a profit instead of a loss. You can run your own figures with the margin of safety calculator.

Why the discount has to vary

A margin of safety is not a fixed number. It should scale with the uncertainty of the business. A stable, predictable company with decades of steady cash flow might justify a 15-20% margin. A cyclical or hard-to-forecast business deserves 40% or more, because the range of plausible outcomes is far wider. The harder a company is to value, the cheaper it must be before you act. In practice this means a utility and an early-stage commodity producer should never be bought on the same discount, even if your central estimate of value looks equally attractive for both.

Margin of safety is humility, expressed in price

The deepest point Graham made is psychological. A margin of safety is an admission that you cannot predict the future precisely, and that even a careful analyst will sometimes be wrong. By building the discount into the purchase, you do not need to be right to avoid disaster; you only need to be roughly right. That is a far more achievable standard than precision. It also disciplines behaviour: when the discount is the rule, you are forced to wait for the market to offer a genuinely attractive price rather than talking yourself into a fair one.

How it connects to position sizing

Margin of safety governs whether to buy; position sizing governs how much. Even a wide margin of safety does not justify betting the portfolio on one idea, because a single unforeseen event can break any thesis. Most disciplined investors cap individual positions at a small percentage of the portfolio and let the margin of safety, not concentration, do the protective work. The two disciplines reinforce each other: a deep discount on a small position protects you twice over, while a thin discount on a large one exposes you on both fronts. This logic flows directly from the wider principles set out in what value investing is.

In short, the margin of safety is the single habit that turns a valuation into an investment decision. Estimate intrinsic value as a range, demand a discount wide enough to survive being wrong, and size the position so no single mistake can be fatal. From here, the natural next step is learning how to find undervalued stocks in the first place, then screening candidates with the Graham Number before sizing your discount.

Written by

Federico Romaldi

Co-Founder, Worthmap

Published: June 6, 2026

Federico is a co-founder of Worthmap, a wealth-intelligence platform built for serious investors. With a background in software engineering and a long-standing passion for value investing, he created Worthmap to bridge the gap between net-worth tracking and investment analysis.