An investment thesis is your filter. Without one, every deal looks interesting. With one, most deals are clearly outside your scope, and the ones inside it get your full attention. Here's how to build one.

Start with what you know

The best angel investments come from investors who understand the domain deeply. If you spent 15 years in fintech, you have pattern recognition that a generalist doesn't. You know which problems are real, which solutions have been tried, and where the market is heading.

Write down:

Industries where you have direct experience
Business models you understand well
Customer types you've been or worked with
Technologies you can evaluate (or have someone who can)

Your thesis should live where your knowledge gives you an edge.

Define your parameters

Be specific about:

Stage: Pre-seed, seed, or Series A? Each requires different diligence depth and check sizes.

Check size: What's your minimum and maximum? This determines which rounds you can participate in.

Geography: Local deals where you can meet founders, or remote deals where you rely on video and documents?

Sector focus: 1-3 sectors where you have genuine expertise. Not "tech" - that's not a sector. "B2B SaaS for healthcare providers" is a sector.

Business model: Do you prefer subscription businesses, marketplaces, transactional models, or are you model-agnostic?

Build your diligence framework

Once you have your thesis, build a consistent process for evaluating deals that fit it:

First screen (15 minutes): Does this match my thesis? Stage, sector, model, geography. If no, pass immediately.
Deck review (30 minutes): Is the problem real? Is the team credible? Are the economics plausible? If two of three are weak, pass.
Deep diligence (5-10 hours): Founder references, financial model review, technical assessment, competitive landscape, customer calls.
Decision: Based on diligence findings, does this meet your criteria? Yes or no.

Having a repeatable process prevents emotional decisions and ensures you evaluate every deal with the same rigor.

Track and learn

After every deal - invested or passed - write down:

Why you said yes or no
What the key risks were
What surprised you during diligence

After 20-30 deals, patterns emerge. You'll notice which signals predicted success and which predicted failure. Your thesis evolves based on real data, not theory.

The most important rule

Your thesis should make you say no to most deals. If you're saying yes to more than 5-10% of what you see, your filter is too loose. A tight thesis means the deals you do invest in get your full attention, your best network, and your deepest diligence.

That focus is what turns angel investing from gambling into a disciplined practice.