Most financial and retirement planning efforts focus on analyzing how much money you will need at retirement or want to accumulate by a particular date. If you save enough on a regular basis and earn some level of returns, your funds will grow to a certain level over a specified period of time. This can be as simple as compound interest.
However, there is another, often ignored, aspect of planning for a financially secure future. What happens as you withdraw money? How long will your money last? The important things to consider are the level of withdrawals and the earnings rate of the funds.
In general, if you withdraw less than what you are earning, your funds will last forever. If you withdraw more than you are earning, at some point you will deplete your assets.
Following is a chart showing how many years your money will last at different withdrawal rates and different earnings rates. The chart assumes the level of withdrawals increases at 4% per year (to cover increasing costs of living) and shows how long your money will last at different rates of return on your money.