Using a real (inflation-adjusted) return lets you enter today's withdrawal amount and get an answer in today's purchasing power, without separately modeling rising prices every year.
The 4% rule is a rule of thumb derived from historical market simulations across many possible return sequences. This calculator instead lets you test your own specific savings, withdrawal, and return assumptions directly — useful for checking scenarios the 4% rule doesn't cover (higher or lower withdrawal rates, different expected returns).
Yes. This tool uses one constant average return, but real portfolios experience ups and downs. A bad sequence of returns early in retirement can deplete savings faster than this simple model suggests (known as "sequence of returns risk"). Use this as a rough estimate, not a precise forecast.