Surely income tax would only apply to additional income. e.g., the higher tax rates would apply only to higher brackets. e.g., 0% on first $20k, 30% on the nex

Surely income tax would only apply to additional income. e.g., the higher tax rates would apply only to higher brackets. e.g., 0% on first $20k, 30% on the next $20k, 40% on the $60k after that, and so on. I think in Australia, the tax-free threshold these days is around $12k.