You can retire safely when you have 25x your annual expenses invested in income generating assets
At a time when many struggle to save enough for a comfortable retirement, there are a few people who can not only retire comfortably but can do so earlier than the expected 65 years old.
Source: Securing an Early Retirement: The Blogosphere’s 7 Best Lessons
My Comments: Generally agree with the points here. Primarily start early and stay disciplined (hard for most to do). Do both and you are pretty much guaranteed – I promise.