Everyday money · General financial education

Opportunity cost

Every use of money has alternatives you then do not take. The value of the best forgone alternative is the opportunity cost.

In more detail

Cash under the mattress avoids account fees and price swings, and gives up interest and purchasing power another use might have had. Conversely, a long contract binds access. This is not about regret; it is a comparison of two paths.

Background

Models often show forgone interest or forgone real purchasing power. Both are assumptions, not forecasts. Inflation quietly reduces the purchasing power of idle cash without a statement line. Compound growth as an alternative is also only a calculation path. Finmon does not rank which path is “right”.

An example

€1,000 sits in a drawer for a year. At 3% price rises, the same notes buy only about €971 of today’s goods. Interest that a balance might have shown is missing too: a calculation, not a rebuke.

A common misconception

If I do not invest it, it cannot cost anything.

Not using money has alternatives: forgone interest and often less purchasing power.

Source: OECD · Financial education. Last reviewed: 2026-11-09. Editorially reviewed on 2026-11-09. Next review 2027-11-09. Version 0.2.0. Finmon explains. It does not advise. Not investment, tax or legal advice.