Cash Buffers: Sizing a Reserve Against Drawdowns

Most guidance treats saving and investing as the same activity at different scales. Build up money, then put it to work.

The question of why save before investing is really a question about sequencing, and the reason order matters has little to do with returns. It has to do with what happens when an unexpected expense arrives while markets are down.

An investor with a cash buffer handles that as an inconvenience. An investor without one becomes a forced seller at whatever price is available, which is a materially worse outcome than the arithmetic of the expense alone suggests.

What the Buffer Protects

The buffer isn't there to earn a return. It's there to prevent a specific sequence of events:

• An unplanned expense arrives, with no notice and a short deadline
• The investment account is the only source of funds
• Markets happen to be down, which correlates with periods of economic stress
• Assets are sold at a poor price, crystallising a loss
• Those assets are absent from the recovery, which is the lasting cost

The final step is what makes this expensive. A withdrawal during a decline removes capital permanently from a portfolio that would otherwise have participated in whatever came next.

How Common a Thin Cushion Is

Household survey data gives a sense of how widely this exposure is held.

The central bank's annual survey of household finances reports that the share of adults who would pay for an unexpected $400 expense with cash or the equivalent was unchanged year on year, as was the share who said they had rainy day funds to cover three months of expenses, with both measures down from their 2021 levels.

The same report notes that relatively small unexpected expenses can be a challenge for families without a financial cushion, which is the practical framing worth keeping. This isn't about large emergencies. It's about ordinary ones landing at an inconvenient moment.

Why the Number Has Stalled

The persistence of the pattern is more informative than its level.

Research work on household resilience notes that for more than a third of adults, an unexpected $400 expense would constitute a financial emergency, and that improving this is treated as an economy-wide issue rather than an individual one.

That figure improved substantially through the 2010s and then plateaued, holding roughly steady across several years of low unemployment. A strong labour market on its own didn't move it, which suggests the constraint is the gap between essential costs and income rather than employment.

For an individual, the useful implication is that a buffer has to be built deliberately. It doesn't accumulate as a by-product of things going well.

Sizing From Your Own Figures

Standard advice offers three to six months of expenses. That's a reasonable starting point and a poor stopping point, because the right figure depends on circumstances that vary widely:

• Income stability, since variable or commission-based income needs a larger buffer than salaried
• Household earners, as two incomes provide partial redundancy that one doesn't
• Dependants, which raise the floor on essential spending
• Notice period and sector, affecting how long a job search might take
• Fixed commitments, such as housing costs that can't be reduced quickly
• Access to other liquidity, though credit is the weakest form of this

The base number should come from twelve months of actual essential spending rather than a budget, because budgets systematically understate what households really spend.

Where to Hold It

The buffer's requirements are availability and stability, not return:

• Instant or short-notice access, since the point is availability under time pressure
• No market exposure, because the buffer is needed precisely when markets fall
• Separate from spending accounts, so it isn't gradually absorbed
• Interest-bearing where possible, since there's no reason to accept nothing
• Reviewed annually against current expenses rather than the figure set years ago

The separation matters more than it sounds. A buffer held in the main current account tends to be spent, and the shortfall goes unnoticed until it's needed.

When to Move On to Investing

The sequencing argument doesn't require the buffer to be complete before anything else happens. Most people build both at once, and there's a reasonable case for capturing employer pension contributions from the start regardless.

What the sequencing does argue for is a floor. Investing an amount that would have to be withdrawn during the next unexpected expense isn't investing, it's a short-term position with a random exit date, and it will be exited at the least favourable moment by construction.

Once the buffer covers essential spending for a defined period, the money above it has a genuinely long horizon, which is the condition every argument for investing depends on. Getting to that point first is what makes the rest of the plan hold together.