What it means
The core insight is that the mix matters more than the individual picks. Decades of practice suggest that the split between shares, bonds and cash explains most of the variation in a portfolio's returns over time, which is why professionals spend so much effort on asset allocation before they discuss specific securities.
Portfolio management is usually described as either active or passive. Active managers try to beat a benchmark by choosing holdings or timing entry and exit, while passive managers aim to track an index cheaply and accept the market return.
The process runs in a loop. You set objectives and constraints, translate them into target weights for each asset class, buy the holdings, monitor performance against a benchmark, and then rebalance back to target when market movements have pulled the weights out of line.
Rebalancing is the part most people skip, and it is where a lot of the discipline lives. If shares rise strongly they become a larger share of the portfolio than intended, which quietly raises risk, so selling some and topping up the laggards restores the intended risk level and enforces selling high and buying low.
Businesses do this too, not just individuals. A company treasury manages a portfolio of deposits, bills and short bonds against rules on liquidity, credit quality and maturity, and the same language of allocation, benchmark and rebalancing applies.
In practice
Real-world examples
Example 1
A charity endowment of $30,000,000 is managed against a policy of spending 4% of the three-year average value each year. The investment committee sets allocation targets, reviews them annually, and instructs the manager to rebalance whenever any asset class drifts more than five percentage points from target.
Example 2
A 34-year-old marketing director holds a workplace pension invested 85% in global equities. Because her time horizon is over 30 years, her adviser leaves the high equity weighting alone during a market fall and simply continues the monthly contributions, which buy more units at lower prices.
Example 3
A manufacturing group's treasury holds $45,000,000 of working capital reserves. Policy limits any single counterparty to 15% of the total and requires that at least half the balance can be turned into cash within seven days, so the treasurer manages maturities and credit exposure much as a fund manager manages holdings.
Think of it
Portfolio management is like packing a balanced picnic basket. You do not just bring twenty packets of crisps. You include sandwiches for substance, fruit for health, and water for hydration, ensuring you are prepared for whatever weather or hunger strikes.
Formula
Calculation
Portfolio return = sum of (weight of each asset class x return of that asset class)
Consider a $2,000,000 portfolio with target weights of 60% equities, 30% bonds and 10% cash. That is $1,200,000 in equities, $600,000 in bonds and $200,000 in cash. Over the year equities return 9%, bonds return 4% and cash returns 2%.
Portfolio return = (0.60 x 9%) + (0.30 x 4%) + (0.10 x 2%)
Portfolio return = 5.4% + 1.2% + 0.2% = 6.8%
In dollars, the gain is 6.8% x $2,000,000 = $136,000, so the portfolio ends the year at $2,136,000. The individual balances are now $1,200,000 x 1.09 = $1,308,000 in equities, $600,000 x 1.04 = $624,000 in bonds and $200,000 x 1.02 = $204,000 in cash.
Equities are now $1,308,000 / $2,136,000 = 61.2% of the portfolio, above the 60% target. Restoring the target means holding 60% x $2,136,000 = $1,281,600 in equities, so the manager sells $1,308,000 - $1,281,600 = $26,400 of shares and moves the proceeds into bonds and cash.Case study
Seen in the real world
Westerbrook Family Trust is a fictional entity used here for illustrative purposes. The trustees had accumulated 41 individual holdings over 20 years, mostly bought because someone recommended them, with no written policy and no benchmark to measure against.
A review found that roughly 38% of the value sat in just three banking shares, that the trust held almost no international exposure, and that nobody could say what return the portfolio was supposed to deliver. The trustees wrote a one-page investment policy: a target of 55% equities, 35% bonds and 10% cash, a benchmark built from three public indices, an annual rebalance, and a rule that no single holding could exceed 5% of the total.
Implementing it took two tax years, spreading the sale of the concentrated banking position to manage the capital gains bill. In this illustrative example the headline return over the following three years was only slightly better than before, but the portfolio's worst quarter was far shallower, and for trustees managing money on behalf of beneficiaries, that reduction in downside was the real prize.
Watch out
Common mistakes
- Confusing a pile of individually sensible investments with a managed portfolio, when nobody has agreed the overall mix, the goal or the benchmark.
- Never rebalancing, so that a winning asset class quietly grows into an outsized position and the portfolio ends up far riskier than the owner intended.
- Judging the manager on raw return without comparing it to a relevant benchmark and to the amount of risk taken to achieve it.
Questions
People also ask
What is the difference between asset allocation and portfolio management?
Asset allocation is one step within portfolio management, the decision on how much goes into each asset class, while portfolio management also covers selection, monitoring, rebalancing and reporting.
How often should a portfolio be rebalanced?
Common approaches are annually, or whenever an asset class drifts more than a set threshold such as five percentage points from its target, with the threshold method usually producing fewer and more meaningful trades.
Does portfolio management only apply to investments?
No, the same discipline is applied to portfolios of projects, products, loans and property, where the goal is again to manage the mix and its combined risk rather than each item in isolation.