T4 Box 18 - Employee's EI Premiums
The software calculates the employment insurance premiums required for each employee, based on the employment insurance insurable earnings in box 24. If the premium withheld from the employee’s salary differs from the amount calculated, override the amount in box 18 and enter the amount actually withheld. Leave the box blank if premiums have not been withheld.
Do not report on the T4 slip the portion of employment insurance premiums paid by the employer.
In the case where the premium withheld differs from the amount calculated, see the T4/RL-1 - Employment Income help topic if you want to make an adjustment.