To step off the corporate treadmill in your 50s or early 60s and maintain anything close to your standard of living, you need a seriously big retirement kitty.
How serious? You'll likely need assets worth 10 to 16 times your salary by the time you leave your job. A 45-year-old making $120,000 who hopes to retire at age 60, say, should already have nearly $700,000 set aside. (See the Retire Early calculator.)
You can get by with less if you'll have other sources of income. If that same 45-year-old has a typical old-fashioned check-a-month pension, for example, he might need only $432,000 in savings to be on track. If you expect to hold down a scaled-back job for your first decade of retirement, you can also get by with less.
If the combination of Social Security, pensions and prudent draws from your savings is enough to cover the expenses on your retirement budget, then you're pretty much home free. Let your retirement adventures begin!