Beta
Also written β · Beta coefficient
How sharply a share moves relative to the market index — beta 1 moves with the index, above 1 amplifies it, below 1 dampens it. The standard measure of systematic risk.
In plain language
Beta answers one question: when the index moves, how much does this share move?
A beta of 1 means it tracks the index. A beta of 1.5 means it tends to move half again as hard in both directions — up 15% when the Nifty rises 10%, down 15% when it falls 10%. A beta of 0.6 means it moves less than the index either way.
It measures only the risk that comes from being in the market at all. The risk of a factory fire or a failed product is specific to the company and does not show up in beta, because an investor can diversify it away.
How it works
Beta is the slope of a regression of the share's returns against the index's returns, usually over one to five years of data.
The pattern is consistent across sectors: banks, metals, real estate and capital goods carry high betas because they depend on the credit and investment cycle. Consumer staples, pharmaceuticals and utilities carry low betas because people buy soap and medicine in a downturn too.
The formula
β = Covariance (stock return, market return) ÷ Variance (market return)
Expected move in the stock = β × move in the index
A worked example
An investor holds three shares. The Nifty falls 12% in a quarter.
| Holding | Beta | Expected move | Value before | Value after |
|---|---|---|---|---|
| A metals producer | 1.6 | −19.2% | Rs 3,00,000 | Rs 2,42,400 |
| A private bank | 1.2 | −14.4% | Rs 4,00,000 | Rs 3,42,400 |
| An FMCG company | 0.5 | −6.0% | Rs 3,00,000 | Rs 2,82,000 |
| Portfolio | 1.11 | −13.3% | Rs 10,00,000 | Rs 8,66,800 |
The portfolio beta is the value-weighted average of the individual betas: (0.3 × 1.6) + (0.4 × 1.2) + (0.3 × 0.5) = 1.11. The portfolio fell about Rs 1.33 lakh where a pure index holding would have fallen Rs 1.20 lakh — the cost of carrying more systematic risk than the market.
Why NISM asks about it
Chapter 12 (Fundamentals of Risk and Return) defines beta; Chapter 10 uses it inside CAPM to set the cost of equity. Expect straightforward "index up x%, beta y, what happens to the stock" calculations, and portfolio-beta questions using weighted averages.
Common exam traps
- Beta measures systematic risk only. A high-beta share is not "riskier" in every sense — a low-beta company can still go bankrupt from a company-specific failure.
- Portfolio beta is a weighted average of component betas, weighted by value, not an average of the numbers.
- Beta works in both directions. A beta of 1.8 is not a promise of outperformance; in a falling market it is the reason the portfolio falls hardest.
- A negative beta is possible — gold and gold miners sometimes show one. It means the asset tends to rise when the market falls.
- Beta is historical and unstable. It changes as a company's debt and business mix change.
Where this is taught
- Series XIX-C · Chapter 5: Introduction to Capital Market Theoryintroduced here
- Series V-D · Chapter 10: Risk, Return and Performance of Fundsintroduced here
- Series XIX-D · Chapter 3: Alternative Investment Funds in India and its Suitabilityintroduced here
- Series XIX-B · Chapter 3: Introduction to Category III AIF Ecosystemintroduced here
- Series XV · Chapter 10: Valuation Principlesintroduced here
- Series XIX-E · Chapter 3: Introduction to Modern Portfolio Theory and Capital Market Theoryintroduced here
- Series VIII · Chapter 3: Introduction to Forwards and Futuresintroduced here
- Series V-A · Chapter 10: Risk, Return and Performance of Fundsintroduced here
- Series X-A · Chapter 16: Portfolio Performance Measurement and Evaluationintroduced here
- Series XVII · Chapter 5: Evaluating Fund Performance & Fund Selectionintroduced here
- Series XIX-A · Chapter 1: Overview of Alternative Investmentsintroduced here
- Series XV · Chapter 12: Fundamentals of Risk and Return
Related terms
- CAPMA model that prices the return an investor should demand from a share: the risk-free rate plus beta times the market risk premium.
- Sharpe ratioReturn earned above the risk-free rate divided by standard deviation — how much reward an investment produced for each unit of total risk its holder had to live with.
- Standard deviationA measure of how far returns typically stray from their own average — the standard statistic for total risk, counting company-specific and market-wide causes alike.
- Systematic riskThe part of an investment's risk that comes from economy-wide forces moving every asset at once — it cannot be diversified away, and it is the only risk the market pays you to carry.
- Market riskThe risk of loss from movements in market prices — one named category in a manager's risk framework, alongside credit, liquidity and operational risk, and the one measured with VaR and stress tests.
- Unsystematic riskThe part of an investment's risk that belongs to one company or one issuer — a strike, a fraud, a downgrade — and which diversification can remove, unlike market-wide systematic risk.
- Treynor ratioRisk premium per unit of market risk — the return a scheme earned above the risk-free rate, divided by its beta rather than by its standard deviation.
- AlphaThe return a fund earned above what its beta and the benchmark say it should have earned — the slice of performance left over once the market has been given credit for its share.
- CAGRThe single smoothed annual rate at which a starting value would have to grow, compounding each year, to reach the ending value over a given period.
- DiversificationSpreading an exposure across holdings that do not move together, so that total risk falls by more than total return does — minimising risk per unit of return.