How to Write an Investment Thesis

An investment thesis is a short written document stating why you are buying a company, what has to be true for it to work, what it is worth, and what would prove you wrong. Write it before you buy, keep it concise, and reread it whenever the price moves so decisions rest on your reasoning, not your emotions.

Where this fits: a written thesis is where the Five Criteria framework becomes a concrete decision, and it is the single most practical tool for the discipline that protects you from cognitive biases.

What an investment thesis is, and why it matters

An investment thesis is simply the written case for owning a particular business. It captures, in your own words, why you are buying, what you expect to happen, what the company is worth, and what would make you change your mind.

It sounds almost too simple to matter. It is, in fact, one of the most powerful tools an investor has, for three reasons.

• It forces honest thinking. Vague conviction survives in your head; it collapses on the page. If you cannot write the case clearly, you do not have one.
• It creates accountability. A written thesis is a record you can check later, which protects you from hindsight bias quietly rewriting what you “always knew”.
• It is your anchor. When the price swings and emotion surges, the thesis gives you something objective to return to. You reread your reasoning instead of reacting to the ticker.

That last function is the most valuable. Most poor decisions happen when price movements override reasoning. A thesis lets reasoning win.

Write it before you buy

The timing is not negotiable: write the thesis before you commit capital.

Writing beforehand forces you to confront the weaknesses in your idea while you can still walk away at no cost. It is far easier to abandon a flawed thesis on paper than to sell a mistake you have already bought and grown attached to.

Writing afterwards produces something different and far less useful: a justification. Once you own something, every instinct pushes you to defend the decision rather than examine it. A thesis written after the fact is rationalisation wearing the costume of analysis.

So the rule is firm. No thesis, no purchase.

The components of a strong thesis

A good thesis does not need to be long, but it should cover the following. Think of these as the sections you fill in.

1. The business in plain English

Describe, simply, what the company does and how it makes money. If you cannot explain the business model in a few sentences a non-expert would understand, that is a warning that it may sit outside your circle of competence.

2. Why it is a great business

Address the first four of the Five Criteria:

• Quality: Does it earn high returns on invested capital?
• Moat: What is the durable competitive advantage, and why will it last?
• Management: Is management capable and aligned with shareholders?
• Balance sheet: Is it financially sound, with manageable debt?

3. What has to be true

State the key assumptions your case depends on. Perhaps the moat holds, margins stay stable, the industry grows modestly. Making these explicit does two things: it clarifies your reasoning, and it gives you specific things to monitor over time.

4. Valuation and the price you will pay

Address the fifth criterion: a reasonable price. Give a sense of what the business is worth, using a discounted cash flow estimate or an FCF yield, and state the margin of safety you require between price and value. A thesis without a view on price is incomplete; a great business bought at any price is not a great investment.

5. What would prove you wrong

This is the section most investors skip, and it is the most important. List the specific developments that would break the thesis: the moat erodes, a key assumption fails, debt balloons, management betrays shareholders. These falsification conditions are what let you sell rationally later and distinguish a genuine mistake from temporary noise.

6. Position size

Note how large a position this will be and why, consistent with your position-sizing rules. Conviction and risk should both inform the size.

Section	Question it answers	Why it matters
The business	What does it do and how does it earn?	Confirms it is inside your competence
Why it is great	Does it meet the first four criteria?	Establishes quality and durability
Key assumptions	What must stay true?	Tells you what to monitor
Valuation	What is it worth, and my margin of safety?	Prevents overpaying
What breaks it	What would prove me wrong?	Enables rational selling
Position size	How much, and why?	Controls risk

Keep it concise

A thesis should be short, usually one to two pages. This is not laziness; concision is a test.

If you cannot state the core case in a few clear paragraphs, you very likely do not understand the business well enough to own it. The discipline of brevity forces you to separate the handful of things that truly matter from the mass of detail that does not. A thesis that runs to twenty pages is often a sign of confusion dressed up as thoroughness.

Peter Lynch’s advice captures the spirit: you should be able to explain, in a couple of minutes and in plain language, why you own something. If your explanation requires a spreadsheet and half an hour, the idea may be too complicated or your thinking too muddy.

Using the thesis after you buy

The thesis is not a document you file and forget. It is a living tool you return to.

When the price falls sharply, reread the thesis before doing anything. Ask the only question that matters: has the business, or has only the price, changed? If the thesis is intact, the lower price may be an opportunity rather than a reason to sell. If a falsification condition has been triggered, you have your answer, and selling is the disciplined response.

When the company reports, check results against your key assumptions. Are they holding? Is the thesis progressing as expected, or quietly deteriorating?

On a schedule, review every thesis at least annually. Does each still meet the criteria you bought it on? Has anything drifted?

This is how a thesis defends you in a market crash: you have a calm, written standard to measure the panic against, so you react to facts rather than to fear.

A short worked example

To show the shape, here is a deliberately simplified, hypothetical thesis. (Company C is invented purely to illustrate the format; it is not a real company or a recommendation.)

Company C. A payments processor that earns a small fee on each transaction across a large network. Why great: high ROIC, a network-effect moat that strengthens as more merchants and users join, owner-operator management holding meaningful stock, and net cash on the balance sheet. Must be true: transaction volumes keep growing modestly; no regulation caps its fees; the network advantage holds. Valuation: my conservative DCF suggests it is worth meaningfully more than today’s price, giving a margin of safety of roughly a third. What breaks it: a regulatory cap on fees, a credible competing network reaching scale, or management diluting shareholders through reckless acquisitions. Size: a standard position, scaled to conviction and the quality of the balance sheet.

Notice how much that compact paragraph does. It states the case, the assumptions, the value and, crucially, the conditions that would end the investment. That is a thesis you could reread in a crash and actually use.

Frequently Asked Questions

How long should an investment thesis be? Short enough to be useful, usually one to two pages. If you cannot make the core case in a few clear paragraphs, you probably do not understand the business well enough to own it. The discipline of concision forces you to separate what matters from what does not.

When should I write the thesis? Before you buy, always. Writing it beforehand forces you to confront weaknesses while you can still walk away, and it removes the temptation to rationalise a purchase after the fact. A thesis written after buying tends to be a justification rather than an honest analysis.

What’s the most important part of a thesis? The falsification conditions, the specific things that would prove you wrong. Most investors write only the bull case. Stating in advance what would break the thesis is what lets you sell rationally later and tells you the difference between a temporary setback and a genuine mistake.

How often should I revisit my thesis? Review it when the company reports, when material news arrives, and whenever the price moves sharply enough to tempt you to act. Rereading the thesis is how you decide whether the business has changed or only the price. An annual full review of every thesis is a sound habit.

Your Next Step

A thesis turns analysis into disciplined action. Put it to work with:

• The Five Criteria scorecard to structure the quality assessment.
• The DCF intrinsic value calculator for the valuation section.
• How to Research Stocks: a step-by-step guide to gather the inputs.

---

About the author: Cameron Hayes is a senior investor relations and finance professional who has worked in IR at Nasdaq Copenhagen-listed companies including Nilfisk and Maersk Drilling. He holds an MSc from Copenhagen Business School and a BCom from the University of Ottawa, and founded Gingernomics to teach individual investors the Five Criteria framework. More about Gingernomics.

The content on Gingernomics is for educational and informational purposes only and does not constitute financial advice. Always do your own research and consult a licensed financial advisor before making any investment decisions. Past performance is not indicative of future results.