An additional enhanced basic personal amount applies to all individuals whose net income is less than the amount at which the 29% marginal federal tax rate begins to apply ($150,473 for 2020). For these individuals, the enhanced basic personal will be $13,229, $13,808, $14,398, and $15,000 for taxation years 2020 through 2023, respectively (and the credit will continue to be 15% of this amount).
For individuals whose net income is in the top tax bracket where the marginal federal tax rate is 33% (net income over $214,368 for 2020), the enhanced credit is not available, and the basic personal amount remains at $12,298 for 2020 (and indexed after that).
For individuals in the 29% tax bracket (net income between $150,473 and $214,368 for 2020), the enhancement to the credit is gradually phased down to zero as net income approaches the top of that bracket ($214,368 for 2020).
(Interestingly, the income limits at which the enhanced credit is phased out or eliminated are based on net income, and not the (sometimes lower) “taxable income”, even though the tax rates themselves apply to taxable income.)