The 4% rule is a common rule of thumb used in retirement planning to estimate how much money you can safely withdraw each year without running out of funds. It is based on historical market performance and assumes a diversified portfolio. While it provides a useful starting point, personal circumstances, market conditions, and inflation rates may affect its applicability. Financial planners may adjust this rate depending on your retirement age, healthcare needs, and other income sources. Always consult with a financial advisor for personalized planning.