We have now integrated into Jurifamille the option to take into account the income of adult children to adjust calculations derived from the child support determination table. The method we followed for calculations follows the jurisprudence established by the Court of Appeal (Droit de la famille-08556 and Droit de la famille-123218) and detailed by Me Michel Tétrault in Droit de la famille, volume 2: L'obligation alimentaire.
The calculation is done by dividing the Total Basic Contribution reported by the determination table by the number of children, thus obtaining a basic contribution per child. For each child, we then perform the required calculations according to the applicable custody arrangements, deducting the adult child's contribution only where it applies.
Certainly, when all children have the same custody arrangement, the shortcut of adjusting the total contribution amount (line 401) can work, but as soon as custody arrangements vary, this leads to inequitable results (which were the source of the two decisions mentioned above).
You will find instructions in the Frequently Asked Questions section of the Help and Documentation, under the heading How to take into account the income of an adult child in child support calculations?.