Why do we treat money differently depending on where it came from?

A gain from a recent trade feels easier to risk than money that was carefully saved over time. A dividend is treated as “income” to spend, while capital is preserved. Losses in one part of a portfolio are viewed separately from gains in another, rather than as part of a single outcome.

Individually, these distinctions can feel sensible. Together, they reveal a pattern.

This is where mental accounting begins to influence behaviour. Rather than viewing money as fully interchangeable, the mind tends to organise it into separate categories. Each category is treated differently, often with its own set of rules. The result is not a single, unified decision process, but a series of smaller ones, each shaped by how the money is perceived.

The idea was first explored by Richard Thaler, who showed that people do not treat all money equally, even when it is economically identical. In one simple example, individuals were more willing to spend money that felt like a “windfall” than money that had been earned or saved. The source of the funds changed the way decisions were made, even though the value remained the same.

In markets, this can lead to inconsistencies across a portfolio. Gains may be taken more freely in one area while losses are tolerated in another. Risk levels can vary depending on how a position is mentally categorised. Decisions that appear rational within each category may not make sense when viewed together.

What makes this difficult to recognise is how natural it feels. Categorising simplifies complexity. It allows decisions to be broken into manageable parts. The challenge is that those parts do not always add up in a coherent way.

You may notice this in yourself when you treat certain gains as “less important,” or when losses are evaluated in isolation rather than in the context of the overall portfolio. There can also be a tendency to assign meaning to different pools of capital, even when that distinction has no bearing on the underlying decision.

Mental accounting does not change the value of money.

It changes how decisions about it are made.

For Further Reading

Thaler, R. H. (1985). Mental Accounting and Consumer Choice. Marketing Science, 4(3), 199–214.