Find the table amount for income, find the table amount for the other parent's income, subtract one from the other and pay the difference.
In order to claim the children on your income tax, the CRA requires that either:
a) the claimant be the support receiver, not the support payer, or
b) both parents are paying support, through the setoff method described above.
Your custody agreement or court order should specify that you have Shared Parenting, that both parents' support amounts are setoff against each other according to section 9 of the Child Support Guidelines. The CRA will require this type of wording in order to allow both/either parent to claim deductions.