No. Unused talk, text, and data from your base plan do not roll over to your next billing cycle.
However, all add ons carry a 30 day validity from date of purchase. For example, your base plan purchased on January 1 will expire on January 31st. Any add ons purchased on January 15 will extend through the base plan billing cycle and expire on February 14.
Sign in to your account to see when your billing cycle ends.