It depends on how many days are on your original ticket.
It costs $88.00 to add a day to a 2-day ticket.
It costs $35.00 to add a day to a 3-day ticket.
It costs $15.00 to add a day to a 4-day ticket.
It costs $10.00 to add a day to a 5-day ticket.
It costs $10.00 to add a day to a 6-day ticket.
It costs $10.00 to add a day to a 7-day ticket.
It costs $10.00 to add a day to a 8-day ticket.
It costs $10.00 to add a day to a 9-day ticket.
(The maximum number of theme park days per ticket is 10.)