How to retire at 40

THE "4 per cent rule" is a bedrock of retirement planning. But does it apply to those who quit working before 65? The rule of thumb holds that retirees who spend only 4 per cent of their investment portfolio annually, adjusted for inflation, will be able to stretch out their savings for the rest of their life.

For example, a US$1 million brokerage account gets you US$40,000 a year to spend.

Lately, the 4 per cent rule has been under assault, with experts warning that the future could bring weaker market returns, an increased life span, or both.