This is discussed further in these posts:
Retire: Two-stage FIRE (part 1)
Podcast: The two-stage FIRE approach
FIRE
Financial Independence, Retire Early (FIRE) is a movement dedicated to the idea that retirement is about having enough assets to sustain you for life, rather than an age at which you stop working. The FIRE movement advocates tight control over lifestyle expenses, a high savings rate and a 4% portfolio drawdown rate upon independence.