 Understanding how much money you're going to need in retirement, or I should say underestimating how much money you're going to need in retirement can lead to inadequate savings. You just won't have saved enough. So you need to be able to calculate what your needs are. Use retirement calculators. Estimate how much you're going to need based on your desired lifestyle, health care costs, and then don't forget to factor in the silent tax. Of course, we know that is inflation.