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NISM-Series-X-B: Investment Adviser (Level 2) · Behavioural Finance in Practice

Prospect Theory and Mental Accounting Explained for NISM X-B

Updated 11 October 2026 · Fact-checked

Prospect theory says people judge outcomes as gains or losses from a reference point, not as final wealth, and feel losses more than equal gains. Mental accounting says people split money into separate mental buckets. Both distort risk-taking and portfolio construction. You solve questions by spotting the reference point, the frame and the bucket.

Understand Prospect Theory and Mental Accounting

Traditional finance assumes investors are rational. They look at total wealth, weigh probabilities correctly and are consistent. Prospect theory, developed by Daniel Kahneman and Amos Tversky, describes how people actually decide when outcomes are uncertain.

The core idea: people do not judge outcomes by final wealth. They judge them as gains or losses relative to a reference point. The reference point is often the purchase price, but it can also be a past peak, a target or an expectation. The same ₹1,00,000 portfolio can feel like a win or a loss depending on the reference point.

Three features matter for the exam. First, loss aversion: a loss hurts more than an equal gain pleases. Second, diminishing sensitivity: the difference between ₹0 and ₹10,000 feels larger than between ₹1,00,000 and ₹1,10,000. Third, the value function is S-shaped: concave for gains (risk averse) and convex for losses (risk seeking). So people tend to take sure small gains early and gamble to avoid realising losses. This links to the disposition effect: selling winners too soon and holding losers too long.

Framing means the way a choice is presented changes the decision, even when the facts are the same. A product described as '90% chance of keeping capital' attracts more than one described as '10% chance of losing capital'. Framing works through the reference point and loss aversion.

Mental accounting, associated with Richard Thaler, is the habit of treating money differently depending on its source, purpose or label. A bonus or gift may be treated as 'fun money' and taken to risky bets, while salary savings stay in safe deposits. Money is treated as non-fungible, though a rupee is a rupee. In portfolios this leads to layered 'bucket' portfolios built goal by goal, ignoring correlations across the whole. Buckets can help discipline, but they can also cause poor overall allocation, such as holding a low-yield deposit while carrying a high-interest loan.

Key formulas to remember

Prospect theory core rule
Value = f(gain or loss from reference point), not f(final wealth)
The reference point decides whether an outcome feels like a gain or a loss.
Loss aversion
Pain of a loss > pleasure of an equal gain
Losses loom larger than equal gains. Do not say they are exactly twice as large; the exam only needs the direction.
Shape of the value function
Gains: concave (risk averse) | Losses: convex (risk seeking)
Explains booking small gains early and gambling to recover losses.
Disposition effect
Sell winners too early + hold losers too long
A result of loss aversion and the purchase price as reference point.
Mental accounting
Money is treated as non-fungible by source, purpose or label
Rational view: all money is fungible and the whole portfolio matters.

How to solve Prospect Theory and Mental Accounting questions

Use this method for any scenario or definition question on prospect theory, framing or mental accounting.

  1. 1Read the scenario and name what the client is comparing against. That is the reference point (purchase price, past high, target).
  2. 2Decide whether the client sees the outcome as a gain or a loss from that point.
  3. 3If it is a gain, expect risk aversion and early profit booking. If it is a loss, expect risk seeking and holding on.
  4. 4Check whether the same facts are presented in two ways. If yes, the issue is framing.
  5. 5Check whether the client separates money by source, purpose or label. If yes, the issue is mental accounting.
  6. 6Match to the exact term in the options. Watch for near-miss terms such as anchoring, regret aversion or overconfidence.
  7. 7Pick the option that treats wealth as a whole, or that corrects the bias, if the question asks for adviser action.

Quickest way: Three-word trigger check

When to use it: When you have under a minute per MCQ and the scenario is short.

  1. Look for 'price paid' or 'break-even': prospect theory, reference point, disposition effect.
  2. Look for 'described as' or two versions of the same offer: framing.
  3. Look for 'separate pot', 'windfall', 'bonus' or 'for this goal only': mental accounting.
  4. Eliminate options that name a different bias, then choose the one that fits the trigger.

Common mistakes in Prospect Theory and Mental Accounting

  • Saying prospect theory says people are always risk averse.

    Students remember risk aversion from traditional theory.

    Fix: Remember the split: risk averse in gains, risk seeking in losses.

  • Treating framing and mental accounting as the same thing.

    Both involve how money is seen.

    Fix: Framing is about how a choice is presented. Mental accounting is about how money is sorted into buckets.

  • Judging outcomes by final wealth in prospect theory questions.

    Habit from return calculations.

    Fix: Always identify the reference point first and see the outcome as a gain or loss from it.

  • Calling the disposition effect a separate theory unrelated to loss aversion.

    It has its own name.

    Fix: Link it: loss aversion plus the purchase price as reference point gives the disposition effect.

  • Assuming mental accounting is always harmful.

    Notes stress the errors.

    Fix: It can help discipline goal-based saving, but it harms when it ignores the total portfolio, correlations or costs such as a loan at higher interest.

  • Mixing up loss aversion with risk aversion.

    Similar-sounding terms.

    Fix: Loss aversion is about feeling losses more strongly than gains. Risk aversion is a preference for lower uncertainty.

Worked examples

Example 1

A client bought a stock at ₹500. It rises to ₹560 and she sells at once to lock in the profit. Another stock bought at ₹400 falls to ₹320 and she refuses to sell, hoping it returns to ₹400. Which concept best explains her behaviour? (A) Anchoring only (B) Disposition effect from prospect theory (C) Overconfidence (D) Mean-variance optimisation

Show the solution
  1. Reference point: the purchase price in each case (₹500 and ₹400).
  2. First stock: ₹560 is above ₹500, so it is a gain. In gains people are risk averse and book profit early.
  3. Second stock: ₹320 is below ₹400, so it is a loss. In losses people become risk seeking and hold on to avoid realising the loss.
  4. Selling winners early and holding losers is the disposition effect, which comes from prospect theory.
  5. Option D is a rational portfolio method, and C does not fit the pattern. Option A mentions only one element, the purchase price, and does not explain the opposite behaviour in gains and losses.

Answer: (B) Disposition effect from prospect theory

Example 2

A client receives a ₹2,00,000 annual bonus. He keeps his salary savings in a bank deposit but puts the entire bonus into a speculative small-cap tip, saying 'it is extra money anyway'. He also carries a personal loan at a high interest rate. What is the bias, and what should the adviser do?

Show the solution
  1. The client treats the bonus differently because of its source. This is mental accounting.
  2. Money is fungible. ₹2,00,000 of bonus has the same value as ₹2,00,000 from salary.
  3. The behaviour also ignores the loan. Repaying a high-interest loan gives a certain saving, while the speculative bet is risky.
  4. The adviser should show the client the whole balance sheet and treat all money as one pool.
  5. Then set the allocation by goals, risk profile and costs, including clearing expensive debt first where suitable.

Answer: Mental accounting. The adviser should move the client to a total-wealth view, address the high-interest loan and allocate the bonus by goals and risk profile.

Exam tips

  • Expect scenario MCQs where you must name the bias. Look for the trigger words: purchase price, framing, bucket, windfall.
  • Learn the pairs: gains with risk aversion, losses with risk seeking. Options often swap them.
  • Know that prospect theory contrasts with traditional finance, which assumes rational use of final wealth.
  • Adviser-action questions usually reward options that widen the client's view to the whole portfolio and goals.
  • With negative marking, skip only when two options both fit; otherwise use the trigger check and answer.

Practice questions from Behavioural Finance in Practice

Prospect Theory and Mental Accounting in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Prospect Theory and Mental Accounting: frequently asked questions

What is prospect theory in simple words?

It says people judge results as gains or losses from a reference point, such as the price they paid. Losses hurt more than equal gains please. So people sell winners early and hold losers too long.

What is the difference between mental accounting and framing?

Framing is how a choice is presented, such as '90% safe' versus '10% risk'. Mental accounting is sorting money into separate buckets by source or purpose. One is about presentation, the other is about how you label money.

Is mental accounting always bad for investors?

No. Goal-based buckets can build saving discipline. It becomes a problem when the client ignores the total portfolio, overall risk or costs such as a high-interest loan.

Why does prospect theory matter for an investment adviser?

It explains why clients panic at losses, book profits early and chase risky bets to recover. An adviser can use this to frame advice carefully, set the right reference points and keep the client on the plan.