Marginal Analysis
Making decisions by evaluating the additional benefit of one more unit versus its additional cost — rather than thinking in terms of averages or totals.
The Idea
Most decisions happen at the margin. You’re rarely choosing “all or nothing” — you’re deciding whether to do a little more or a little less of something.
Key Principles
- Marginal benefit: The additional gain from one more unit
- Marginal cost: The additional cost of one more unit
- Optimal point: Where marginal benefit equals marginal cost
- Diminishing returns: Each additional unit typically yields less benefit than the previous one
Examples
- Business: Should we produce one more unit? Compare the revenue from that unit against the cost of producing only that unit (ignore fixed costs)
- Learning: An extra hour of study yields less benefit than the hour before it. At some point, sleep yields more marginal benefit
- Sunk cost fallacy: Past costs are irrelevant to marginal decisions — only future costs and benefits matter
How to Apply
- Ask “What is the next unit giving me, and what does it cost?”
- Ignore sunk costs — they don’t change at the margin
- Stop when marginal cost exceeds marginal benefit (not when total benefit is still positive)