What is the life of a digital certificate?

The certificate expires 27 months after it was originally issued or recovered. If the customer uses the digital certificate during the last 100 days of this time period, the certificate will be updated automatically. Once updated, the certificate will be renewed for another 27 months. This renewal process continues indefinitely. If the certificate is not used by the customer during that 100-day period, it will expire and the customer must use either self recovery or must have an EBC-assisted recovery.

USPTO FAQ - Questions and Answers (30JAN2008)