The $2.6-billion stadium was slated to be ready for the 2019 season, but the rainy winter pushed that back to the 2020 season.
Developers said the rainfall delayed the mass excavation phase. Rams COO Kevin Demoff said economics were not a factor in the decision, he said the decision came based on delivering a "world-class stadium at the highest quality possible."
The Chargers also released a statement regarding the delay.
"Construction is our family business, so we understand the challenges that come with a project of this magnitude. At StubHub Center we are creating an unparalleled environment for watching NFL football. We think Charger fans will enjoy our three years in Carson."
The 2021 Super Bowl will be hosted at the stadium, which is expected to have a capacity of 80,000. The Rams hope the delay won't impact the ability to host the Super Bowl.
A team would need 2 years in the stadium before they're allowed to host the event there, but the NFL could sign off to make it a special case in order to let them host the event.
The Rams have been temporarily playing at the Coliseum in Exposition Park while the Chargers were slated to temporarily play at the StubHub Center in Carson.