Taxable income is what’s left after stripping exempt items (most foreign pensions, certain interest, the first slice of capital gains) and allowable deductions (retirement contributions, qualifying medical scheme fees, donations to PBOs) from your gross income. The bracket rates apply to taxable income, not to gross or to take-home.
For salaried employees, the IRP5 already shows most of this — taxable income is usually code 3699 minus codes 4001/4006 (retirement deductions). Self-employed and provisional taxpayers compute it from scratch on the ITR12: business income minus business expenses, then personal deductions on top.
Some income is taxable but reported separately. Lump sums from retirement funds, severance pay, and certain capital gains have their own rate tables — they’re not added to ordinary taxable income. Confusing the two is the most common ITR12 error and usually shows up as an unexpected amount owing.