Risk Management

Return is what everyone talks about. Risk is what professionals think about. An old saying in fund management goes: take care of the losses and the gains will take care of themselves. This lesson covers the key tools for measuring, limiting and steering risk – from the size of a single position to the question of how safe a retirement plan is.

Rule number one: survive#

A 50% loss needs 100% to recover; a 90% loss needs 900%. A total loss can’t be recovered at all. Hence the most important rule of risk management: avoid losses you can’t recover from – financially or psychologically.

It sounds trivial but is broken all the time: by investors who put a large share of their wealth into one stock, who speculate with leverage or who invest money they’ll need in two years.

Position size: the most important lever#

How much you put into a single investment often matters more than which investment you pick. Two common approaches:

1. Fixed caps: no single stock above, say, 5% of the portfolio, no sector above 20%. Broad index funds are exempt, since they’re already diversified.
2. Risk-based sizing: decide how much you’re willing to lose per position – often 0.5–2% of total wealth – and derive the position size from the distance to your stop-loss.

The calculator shows the logic: the tighter the stop, the larger the position may be – and vice versa. It also shows a trap: with very tight stops, positions become huge on paper. In practice, a stop doesn’t protect against price gaps, as explained in the lesson on order types.

The Kelly criterion#

The question of optimal bet size has long fascinated mathematicians. In 1956, John Kelly of Bell Labs published a formula that, given known odds, calculates the fraction of capital that maximises long-term growth. The Kelly criterion carries two key messages:

• Betting more than “Kelly” makes you grow more slowly in the long run and risks ruin – even with an edge.
• Because nobody knows their odds exactly and people tend to overestimate them, practitioners use only a fraction, such as half-Kelly.

The many faces of risk#

An underrated concentration risk is your employer. Working for a company and owning lots of its stock means a crisis can cost you your job and your savings at once. When Enron collapsed in 2001, many employees lost their retirement savings exactly that way.

Sequence risk: when losses happen matters#

While you’re still contributing, the order of good and bad years doesn’t change the end result of a lump sum. Once you withdraw regularly, such as in retirement, it does. A crash right at the start of the withdrawal phase forces you to sell shares at low prices – shares that are then missing for the recovery. This sequence-of-returns risk can sink a plan even when the average return is fine.

Remedies include a cash or short-term bond buffer for the first years of withdrawals, a more conservative allocation around retirement and flexible withdrawal rules – taking a little less in bad years.

Thinking in scenarios#

Averages hide risks. Professionals therefore ask: what happens in a bad scenario?

• Historical stress tests: how would my portfolio have done in 2008, 2020 or 2022?
• Hypothetical scenarios: stocks −40% plus six months without a job – is my emergency fund enough? Would I have to sell?
• Pre-mortem: imagine the investment has failed three years from now. What most likely happened?

Summary#

Good risk management thinks about losses first. Position size is the biggest lever, caps prevent concentration, and Kelly shows that betting too much hurts even with an edge. Risk has many faces – from liquidity and counterparties to the order of returns during withdrawals. Those who think in scenarios and build a solid foundation outside their portfolio can weather hard times.