Question: I am preparing an individual income tax return and am mystified as to where the Adjusted taxable income amount is coming from. 

This person only has interest, dividends and trust distribution – taxable income = $172,357

Adjusted taxable income is showing as $622,874,

Solution: ATI consists not only from taxable income. Please see screenshot below.You may also check and verify to ATI calculator on ATO site https://www.ato.gov.au/calculators-and-tools/income-tests-calculator/