In mean-variance optimization, the Efficient Frontier traces the upper boundary of all feasible portfolios in risk–return space. Each portfolio on the frontier offers the best possible expected return for its level of risk (as measured by volatility or variance). Portfolios inside the frontier deliver a lower return for the same level of risk or higher risk for the same return.
To construct the frontier, analysts estimate expected returns, volatilities, and correlations among assets and solve an optimization problem to identify the set of allocations that are not improvable in the mean-variance sense. The frontier is typically plotted with risk (volatility) on the horizontal axis and expected return on the vertical axis, helping investors compare candidate allocations and their risk‑return trade-offs under the given assumptions. In practice, feasibility constraints, estimation error, taxes, and transaction costs can cause real‑world portfolios to lie inside the frontier rather than on it. When a risk‑free asset is available, a straight line from the risk‑free rate to a point on the frontier (the tangent portfolio) defines a commonly discussed risk‑return mix under certain assumptions.
The concept is central to Modern Portfolio Theory and is used in portfolio optimization and asset allocation to benchmark potential allocations against the best feasible trade-offs available from the input assumptions.
An analyst compares several proposed allocations and notes which lie on the efficient frontier to illustrate the available risk‑return trade-offs under the given assumptions.
Modern Portfolio Theory · Mean-variance optimization · Portfolio optimization · Risk (volatility) · Expected return · Capital Market Line