Slow wage growth and slow economic growth add up to slow revenue growth and, almost inevitably, a budget deficit. The Treasurer's only option if he wants to rescue his promised surplus, or his credibility, is to cut or delay government spending. The exact opposite of what a struggling economy needs. Even RBA governor Philip Lowe is calling on the government to boost public spending and stop relying on interest rate cuts to boost the economy.

Much has been made about how few monetary policy "bullets" the RBA has left. With official interest rates at 1.25 per cent there is literally not much more they can do if the domestic or international economy doesn't pick up soon. But there's been far less discussion about how to make best use of our fiscal policy "bullets".

Cutting public spending to protect Frydenberg's premature promise of a budget surplus would be a very bad way to enter an economic slowdown: it's the equivalent of pouring water on a fire that's struggling to take hold. But rushing to pass the $95 billion stage three tax cuts that don't kick in until 2024 – half of which flow to the top 20 per cent of income earners – is like leaving the entire wood supply out for the winter because you are confident it won't rain.

No one knows when the next GFC will hit, or the next natural disaster. Treasury has spent the last six years forecasting that wage growth will pick up "soon". While no one knows what the future holds, with rising unemployment and interest rates at record lows, the last thing this Parliament needs to do is pass enormous income tax cuts that do nothing to help us in the short term and cause us nothing but harm in the long run.

Two months ago, Treasury said we were in for smooth sailing. They were wrong. And two months ago the Treasurer said that with so much clear sailing ahead of us that we could afford to lock in big future tax cuts. He was wrong too. But in three years' time, after the Coalition's been in power for nine years, wage growth might finally have picked up, unemployment might finally be below 600,000 and unemployment benefits might have finally risen in real terms. If that's the case, maybe then, it would be a good time to cut taxes for high income earners.

But just in case Treasury's forecasts are completely wrong again, and we stay on the low wage, low growth trend the Coalition has put us on – wouldn't it make sense to wait until the future arrives before we spend $95 billion on future tax cuts? Let's hope the Senate thinks so.

Richard Denniss is chief economist at The Australia Institute.