Michael Schumacher will retire from Formula 1 at the end of the 2012 season, the 43-year-old German announced on Thursday at Suzuka. Following last week's announcement that the seven-time world champion will be replaced by Lewis Hamilton at Mercedes, Schumacher called a press conference along with the team in Japan to call time on a career that has spanned 21 years and more than 300 races. Speaking of his decision, Schumacher said: "We did not achieve our targets but I can be happy about overall achievements in my career. "I would like to thank Daimler, Mercedes-Benz, the team, my engineers and my mechanics for the trust they put in myself. "I would like to concentrate now on the end of the season and enjoy those races with you." Schumacher added that he had felt his energy and enthusiasm had begun to wane, just as it did when he quit Ferrari and the sport the first time at the end of 2006. "I have been thinking for quite a while [about this]," he said. "We had a three-year agreement, hard to keep motivation and energy - it's natural you think about this more than when you are young. "I have had my doubts for quite a while whether I had energy to [carry on]. I said in 2006 my battery was empty and now I am in the red zone. I don't know if there is time to recharge them - but I am looking forward to my freedom. "I have no hard feelings. In a different way we achieved a great deal... "Now I will do exactly as I did the first time - to finish and focus 100 per cent on what I do." Speculation had linked Schumacher to a move to Sauber, where he began his world championship-level career with the Mercedes-backed Swiss-team's endurance prototype squad in 1990, but that proved wide of the mark.