While there is a presumption that a payor’s income as it appears on line 150 of the income tax return be used for the purposes of determining the quantum of support, information about the payor’s current income maybe of use to a court to give an more up-to-date information about the payor’s income. Please see the link below for the Younghusband  and Younghusband case:
https://www.canlii.org/en/on/onsc/doc/2013/2013onsc6550/2013onsc6550.html?resultIndex=1