Mental accounting

A rupee from salary, a rupee from a tax refund and a rupee won in a lottery are the same rupee. Mental accounting is the habit of treating them as if they were not.

The concept was developed by Richard Thaler (the workbook dates it to 1999). People code, categorise and evaluate money by grouping it into separate mental accounts — by its origin or its intended use — and treat those accounts as non-fungible.

Fungibility, in the workbook's footnote, is the fact that all money is interchangeable and has no labels. Mental accounting ignores it, and that leads to sub-optimal decisions. Thaler's recommendation: treat all money the same, regardless of origin or use.

The workbook classifies mental accounting as a cognitive error — specifically an information-processing bias — and describes how it shows up:

• People link spending to specific budgets.
• They take more risk with money seen as a windfall or lottery winnings.
• They spend non-regular income extravagantly; treating salary differently from tax refunds and bonuses leads to irrational spending.

In portfolio terms, investors think of wealth as buckets — retirement, children's education, marriage. That helps them keep a tab on each goal, but it often leads to asset choices within each bucket that would have been avoided had they considered all their investments together and optimised the portfolio as a whole.

Illustrative figures. The Iyers have three "accounts" in their heads:

The FD and the loan. Viewed as one balance sheet, they are paying 10% to borrow ₹5 lakh while lending ₹5 lakh at 7%. Using the FD to repay the loan would save about ₹15,000 a year in the first year (₹50,000 of interest paid versus ₹35,000 earned) — and the education goal could be funded by redirecting the EMI into a dedicated investment. The label "don't touch" is what stops them.

The bonus. The same couple would never put ₹2 lakh of salary savings into a single unresearched small-cap. Because it arrived as a bonus, it goes into a mental account with a much higher risk tolerance.

A portfolio manager drafting their Investment Policy Statement would look at total assets, total liabilities, goals and risk capacity together — which is exactly the correction the workbook describes.

Chapter 14 (Behavioural Finance), section 14.3.2, covers mental accounting among the cognitive errors, with Thaler's definition and the goal-bucket example. A Chapter 14 sample question asks which theory says people treat money differently depending on its origin and intended use — mental accounting. Expect it in bias-classification and matching questions.

• Mental accounting is associated with Richard Thaler. Prospect theory is Kahneman and Tversky; bounded rationality is Herbert Simon.
• It is a cognitive error (information-processing bias), not an emotional bias.
• The fix is fungibility — treat all money as interchangeable, and optimise the whole portfolio.
• Goal buckets are not wrong in themselves — the workbook says they help people keep a tab — but choosing assets bucket by bucket can produce a worse overall portfolio.
• Windfalls attract more risk-taking under mental accounting; the sample question's wording is "depending on factors such as the money's origin and intended use".