Cash flow: the number that determines whether your finances work

Cash flow is the difference between the money coming in and the money going out over a period of time. Positive cash flow means more comes in than goes out. Negative cash flow means the opposite — and it's only sustainable for so long before something has to give.

Positive cash flow doesn't mean you're rich

A household earning $60,000 a year with $50,000 in expenses has $10,000 in positive annual cash flow. They can save, invest, and build financial security. A household earning $120,000 with $125,000 in expenses is technically earning twice as much — but their financial situation is getting worse each month.

Income creates the potential for financial security. Cash flow determines whether that potential is being realised.

The two levers of cash flow

You can improve cash flow in exactly two ways: increase income, or reduce expenses. That's it. Every budgeting strategy, every financial advice framework, every "money hack" is a variation on one of these two levers.

Most people focus almost exclusively on reducing expenses because it feels more immediately controllable. But income growth — through skills development, career progression, or additional income streams — has a ceiling that's much higher than expense reduction.

Fixed vs variable cash flow

Some outgoings are fixed: rent, mortgage payments, loan minimums. You can't easily change these in the short term. Others are variable: groceries, entertainment, dining out. Budgeting primarily applies to variable expenses.

A common mistake is trying to cut fixed costs when they're actually not negotiable, while ignoring variable costs that are more flexible. Audit both — sometimes "fixed" costs are more changeable than assumed (can you refinance? negotiate a lower rate? downsize?), and sometimes variable costs are higher than realised.

How to see your cash flow clearly

Total your after-tax income for a month. Total all your actual expenses for the same month (including irregular ones, amortised). The difference is your cash flow. Do this across three months and average it — a single month can be misleading.

If the number is close to zero or negative, that's the most important thing to address in your financial life before anything else. Savings, investments, and goals all require positive cash flow first.