Opening day of the 49ers’ offseason workout program will be April 15, a day before the regular-season schedule is unveiled for the reigning NFC champions.

The 49ers’ lone, mandatory minicamp will be June 11-13 to conclude the nine-week offseason program, the NFL announced Thursday. Organized team activities will take place May 21-23, May 28-30 and June 3-6.

None of the offseason workouts are expected to be open to the public at the 49ers’ Santa Clara facility.

The league is slated to announce the regular-season schedule on April 16. This will be the 49ers’ 43rd and final season playing at Candlestick Park, assuming their new stadium in Santa Clara remains on track to open in 2014.

Aside from their NFC West rivals — Arizona, Seattle and St. Louis — the 49ers will host Atlanta, Carolina, Houston, Indianapolis and Green Bay. The 49ers’ road schedule features trips to Arizona, Seattle, St. Louis, New Orleans, Tampa Bay, Tennessee, Washington and Jacksonville (in London on Oct. 27).