The frequency in which maintenance fees have to be paid varies from country to country. Some countries will require a yearly payment (e.g. China); others may charge once every five years. Fees in the United States must be paid at 3.5, 7.5 and 11.5 years.
Protecting patents for the entire term of protection (in general, 20 years) may prove to be an expensive undertaking especially since maintenance fees tend to increase the longer the protection is maintained. Please refer to your local patent's office guidance for more information on maintenance fees and payment frequencies.