In an ideal world, child support should be recalculated each time the parties' incomes change. This is because a change in income will almost certainly result in a change to the parties' share of section 7 expenses, and will impact the base child support that should be paid, if the payor's income changes.
Of course, a change to the access or parenting of the children may also result in the base child support having to be recalculated.
If the child support is being paid pursuant to a Court Order, or a written agreement that was prepared with the assistance of a family lawyer, the Order or the agreement will specify the incomes of the parties so as to give an indication as to why the child support payable is the amount that it is.
It is now mandatory for all child support Orders to include clauses that:
a) Require the parties to provide each other with financial disclosure each year;
b) Permits either of the parties to register the Order with the Maintenance Enforcement Program; and
c) Specify whether the Recalculation Program may be used by the parties to recalculate the child support payable.
When a party receives the other party's financial disclosure, the parties can then determine whether they wish to recalculate child support. Some Orders specify how and when child support is to be recalculated each year.
If the payor of child support is providing his/her full financial information to the receiving party each year, it would be wrong for them to simply assume that it is for the recipient of the child support to raise the issue of an increase of child support.
There are enough websites available to parties to enable them to calculate child support, that pleading ignorance to the amount of support that should have been paid is unlikely to be accepted by a Court. The best way to avoid having to face an Application for arrears of child support is to ensure that one is always paying the appropriate amount of child support. So, if one obtains an increase in income, and if one's Order or agreement does not have a procedure for recalculating child support, a Court is likely to determine that increasing the child support immediately is the appropriate thing to do.
Likewise, if one's income decreases, that party should make an Application as soon as possible to have the child support adjusted. This is because, normally, a Court will not backdate a lower amount of child support to a date that is prior to the filing of the Application.