In simple terms, one can retire when one's annual passive income is more than one's annual expenses. A common rule of thumb for the sum needed to retire is the rule of 25 - based on the assumption of a 4% yield, your net worth should be 25 x annual expenses before you can FIRE. So let's say you are a lean spender who spend $1000 a month, theoretically you would need 25 x 12000 = $300,000 This theory has many assumptions. It assumes: 1) Spending remains the same and predictable Which means zero inflation and minimal lifestyle changes. At different phase of life, our lifestyle may change, our spending may change to match our expectations on quality of life. At some point in time when we are old and need hospital care or stay in a home, the expenses are often not predictable. The younger we choose to...