If you add members to the team as the team administrator, you will be charged the subscription fee per member, depending on your chosen plan and the time at which the member was added.
For example, If you are on the monthly Premium subscription for $9.95/month and add a team member to your plan, you will have to pay an additional $9.95/month.
The bill is also adjusted keeping in mind when the member was added. For example, if you add a member after half of your subscription duration has passed (15 days for a monthly subscription), the subscription fee will be adjusted and you will be charged 50% less. Depending on when you add a team member, you will be charged accordingly.