A simple rule of thumb for early retirement, aimed at anyone planning their finances.

• To find your target, take the monthly income you want in retirement and multiply it by 200.
• Want $5,000 a month? You'd need $1 million invested.
• The math works if you earn 6% a year on your savings, which covers the income without touching the original nest egg.
• This is the switch from the earning-and-saving years to living off passive income.

Outlook: Hitting the target depends on steadily earning that 6% return, so market conditions will make or break the plan.