Everyone knows that whatever you borrow has to be paid back. What’s more, you have to keep paying interest on the debt until it is paid back. Parents know they have to get any home loan paid back before they retire.

What common sense doesn’t tell you is that there’s a two-way relationship between the budget and the economy.

The trouble with a family is that eventually it dies. The kids grow up and start families of their own, then mum and dad pop off. But governments don’t die. The nation’s government acts on behalf of all the families in the country. There are always some families dying, but always others taking their place.

This is why families have to pay back their debts, but governments don’t – and often choose not to. Because governments go on and on, the main way they get on top of their debts is by waiting for the economy to outgrow them, so the size of their debt declines relative to the size of the economy.

Remember, unless you add to it, a debt is a fixed dollar amount, whereas the size of the economy – gross domestic product – grows with inflation and “real” economic growth.

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The final thing making government budgets different from family budgets is that a particular family’s budget is too small to have any noticeable effect on the economy, whereas the federal budget is so big – about a quarter the size of the economy – that changes the government makes in its spending and taxing plans can have a big effect on an individual family’s budget and indeed, many families’ budgets.

But it also works the other way: what happens to one family won’t have a noticeable effect on the budget, but what happens to many families – say, everyone’s getting bigger pay rises, or many families are cutting back because they’re having trouble coping with the cost of living – certainly will affect the budget.

What common sense doesn’t tell you is that there’s a two-way relationship between the budget and the economy. The budget can affect the economy, but the economy can affect the budget.

Whenever a treasurer announces on budget night that he (one day we’ll get a she) is expecting the budget deficit to turn into a surplus, the media usually assume this must be because of something he’s done.

Possibly, but it’s more likely to be because of something the economy did. In this month’s budget, it’s because the economy’s been growing strongly, leading families and companies to earn more income and pay more tax on it.

Because many in the media imagine the government’s budget is the same as a family’s budget, they assume that budget deficits are always a bad thing and surpluses a good thing.

Not necessarily. If the budget was in surplus during a recession, that would be a bad thing because it would mean that, by raising more in taxes than it was spending, the budget would be making life even harder for families.

Only when the economy’s growing too fast and adding to inflation pressure is it good to have the budget in surplus and so helping to slow things down. And deficits are a good thing when the economy’s in recession because this means that, by spending more than it’s raising in taxes, the budget’s helping to prop up the economy.

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But not to worry. When the economy goes into recession, the budget tends to go into deficit – or an existing deficit gets bigger – automatically. Why? Because people pay less tax and the government has to pay unemployment benefits to more people. Economists call this the budget’s “automatic stabilisers”.

Hidden away in the budget papers you find Treasurer Jim Chalmers quietly admitting he has no intention of trying to pay off the big public debt he inherited. His “overarching goal” is to “reduce gross debt as a share of the economy over time”.

For a family, a $4 billion surplus is an unimaginably huge sum of money. But for a federal government, it’s petty cash.

Ross Gittins is the economics editor.

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