The Dutch goalkeeper joined United in 2005 from Fulham and has gone on to make over 240 appearances for the club.
He told sport-promotion.nl: "I cannot really identify a time when it [the decision] happened. Let's just say that it was playing on my mind from the moment Annemarie had her stroke.
"She has fought back from it. We decided on another year in England and thus to stay at Manchester United.
"But, once engaged in the season, the thought of saying goodbye started to gnaw a bit more emphatically.""One minute you're out. The next, you question it again. I thought about stopping, maybe a year ago.
"It is a difficult process. After a defeat, I thought differently than after playing a few good games in a row.
"My age played no role. I am 40 years old, but I still feel fit.
"And then the decision came suddenly. Do not ask me how or why, but suddenly you know. That was sufficient.
"The time has come to devote greater attention to my family - although they have never complained. Everyone in the family has indeed always had to focus on me, but we have also had a lot in return.
"Suddenly you just know it’s the time to go, it is time to spend more time with your family."
United goalkeeping coach Eric Steele has paid tribute to the 'keeper: "He has been a fantastic servant," Steele told Radio Manchester. "I was very lucky. I worked alongside Peter Schmeichel at Villa and I worked with Edwin for two and a half years.
"That penalty save in Moscow has elevated Edwin alongside Peter."During his time at Old Trafford, Van der Sar won one Premier League three times, Champions League once, League Cup once, Community Shield three times and the Club World Championship.