LOS ANGELES — After 20 years in a Lakers uniform and a lifetime in basketball, Kobe Bryant determined that his aching body and his passion for the game had both grown weaker than his excitement about the future.

That’s when Kobe decided he could only wait a few more months to begin his life after the Lakers.

Bryant announced Sunday that he will retire after this season, ending a landmark 20-year NBA career spent entirely with Los Angeles. He was serenaded with cheers throughout the struggling Lakers’ 107-103 loss to Indiana, beginning his farewell tour through the league with a clear mind and a curiosity about his next chapter.

“I had to just accept the fact that I don’t want to do this anymore, and I’m OK with that,” the dry-eyed, smiling Bryant said after the game.

The 37-year-old Bryant made the long-anticipated declaration in a post on The Players’ Tribune on Sunday, writing a poem titled “Dear Basketball.”

“My heart can take the pounding. My mind can handle the grind. But my body knows it’s time to say goodbye,” wrote Bryant, the third-leading scorer in NBA history. “And that’s OK. I’m ready to let you go. I want you to know now. So we both can savor every moment we have left together. The good and the bad. We have given each other all that we have.”

When the Lakers hosted the Indiana Pacers on Sunday night, fans expecting an unremarkable regular-season game for the struggling home team instead received a letter from Bryant in a black envelope embossed with gold.

“What you’ve done for me is far greater than anything I’ve done for you,” Bryant wrote. “I knew that each minute of each game I wore purple and gold.”

The theatricality of Bryant’s announcement fit a dramatic career that has included five championship rings and 17 All-Star selections during two decades with the Lakers, giving him the longest tenure with one team in NBA history.