How much will you receive from your sources? Social security and pension plans are among the most popular outside funds for retirees. Head to the Social Security Administration’s website and online calculator to help you work out what you will receive in benefits. Once you know what you’ll be receiving from Uncle Sam, you can decide how much you’d like to invest. A helpful trick to determine this number is to take the amount from your outside resources and subtract that from your disposable income. This number should tell you about how much you’ll need from your investments.