Margin of Safety and Valuation Ranges
How to turn an uncertain valuation into a decision, using bear, base, and bull scenarios, a probability-weighted value, and a margin of safety between the price you pay and the value you estimate.
The short version
Because value is uncertain, careful investors estimate a range: a bear case where things go poorly, a base case, and a bull case where they go well. Weighting the scenarios by how likely you think they are gives an expected value. A margin of safety means only buying when the price is well below your estimate of value, so that errors and bad luck don't turn into big losses. Warren Buffett has written that if a stock's value is only slightly above its price, he isn't interested in buying. For STU Corp at $50, the base case offers no margin of safety at all.
By the end of this lesson, you'll be able to
- Build bear, base, and bull scenarios and a probability-weighted value
- Explain the margin of safety and why it matters
- Apply a margin of safety to judge whether a price is attractive
Why this matters
The last lesson showed that STU Corp's estimated value could reasonably be anywhere from about $35 to $62 a share. A range like that doesn't tell you what to do on its own. This lesson turns it into a decision rule at the heart of value investing: demand a margin of safety.
Bear, base, and bull
Instead of one set of assumptions, build a few complete stories about the future, each with its own growth, risk, and long-run assumptions:
| Scenario | The story | Growth, years 1 to 5 | Discount rate | Long-run growth | Value per share |
|---|---|---|---|---|---|
| Bear | The biggest customer cuts orders and compatible cartridges arrive | 5% | 10.8% | 2% | $28.88 |
| Base | Steady progress, as in the DCF lesson | 10% | 9.8% | 3% | $44.69 |
| Bull | Subscriptions keep surging and the advantage holds | 14% | 8.8% | 3.5% | $66.94 |
If you judged the bear and bull cases each 25% likely and the base case 50% likely, the probability-weighted value would be 0.25 × $28.88 + 0.5 × $44.69 + 0.25 × $66.94 = about $46.30. The probabilities are judgments, not facts, but writing them down makes your reasoning explicit and open to challenge.
The rest of this lesson is for members
Still to come in this lesson: The margin of safety, the key takeaways, and 2 quiz questions with explanations.
Membership opens every lesson in the curriculum, the capstone projects, the interactive tools, and the members-only channels in the Hyperion Entities Discord. The first lesson of every module stays free.
Go deeper
- Scenario Analysis: Bull, Base, and Bear CasesValuation and Modeling (depth track)
- Probability and Expected ValueMath and Statistics for Investors (depth track)
- Position SizingPart 5: Building a Portfolio
Notes and sources
- Berkshire Hathaway Inc.. Warren E. Buffett, 1992 Letter to Shareholders. Checked 2026-10-01.