Modern Portfolio Theory (MPT) is a framework for thinking about how to combine assets to achieve the best possible risk-return tradeoff. It emphasizes diversification so that a portfolio’s overall risk may be lower than the sum of individual risks.
Using mean-variance optimization, MPT seeks portfolios that offer the highest expected return for each level of risk, forming the efficient frontier. In practice, analysts input expected returns, asset variances, and covariances to calculate an allocation that minimizes portfolio variance for a target return, or maximizes return for a target level of risk. If a risk-free asset is present, the theory identifies a tangent portfolio on the frontier and the Capital Market Line, which helps describe the best feasible combinations of risky assets with the risk-free rate.
MPT relies on estimated inputs that can be unstable, such as expected returns and correlations. It assumes normally distributed returns and rational behavior, and treats risk as portfolio standard deviation, which may understate tail risk or non-normal events. Therefore it is a guiding framework for asset allocation and diversification rather than a guarantee of outcomes. Variants and extensions address estimation error, non-normal risks, and dynamic adjustment.
A financial planner uses Modern Portfolio Theory to select a diversified mix of assets that lies on the efficient frontier for a stated expected return.
Efficient Frontier · Mean-Variance Optimization · Diversification · Asset Allocation · Risk-Return Tradeoff · CAPM (Capital Asset Pricing Model) · Covariance