My dad is paid hourly but sometimes he works over-time. His employer issues his T4 in Feb 2020. He has $50K in RRSP he never deducted. Let BPA mean Basic Personal Amount.
But 2019 isn't over, and he can't know his exact 2019 Annual Income and UD now. So how can he fill out line 1 now?
He shouldn't wait cause processing T1213 takes at least 6 weeks. "If approved, the CRA will provide a Letter of Authority (typically within four to six weeks of submitting Form T1213) that would be provided to your employer as confirmation to reduce tax withholdings."