Five mental models for thinking about money

Charlie Munger popularized the idea of 'mental models' — reusable frames you apply to new problems instead of starting from scratch each time. For personal finance, five simple models cover 90% of the decisions you'll face. Once you internalize them, most money questions answer themselves.

1. Opportunity cost

Every dollar spent is a dollar not invested. Every dollar not invested is a dollar not compounding. Before any discretionary purchase, ask what that money could have grown into over 30 years at an average return. Not to guilt yourself — to accurately price the tradeoff. A $20,000 car loan is a ~$150,000 decision over 30 years.

2. Guaranteed vs. expected return

Paying off a 20% credit card is a guaranteed 20% return. Investing in stocks is an expected 7–10% return with significant variance. Guaranteed beats expected on equal or better terms. This is why debt payoff should almost always come before investing when the interest rate is high.

3. Regret minimization

When two financial choices look similar on paper, pick the one you'd regret less if it went badly. Jeff Bezos used this to decide whether to start Amazon. Most of your money decisions aren't about maximizing — they're about minimizing the emotional cost of being wrong.

4. Time > money (sometimes)

Some purchases buy back time: a cleaner, meal prep, a shorter commute, an assistant. Some purchases cost time: complicated stuff, commuter cars, status items you have to maintain. Time is the only truly non-renewable currency. Spending money to get time back is one of the few trades that rarely feels wrong in retrospect.

5. Incentive alignment

When someone gives you financial advice, ask how they get paid. A commissioned insurance salesperson giving you insurance advice is not evil — they're responding to their incentives, which happen to point away from your interest. A fee-only fiduciary advisor has the cleanest incentive structure. Always know who's paying whom.