The Rule of 72 Do you know how long it may take for your investments to double in value? The Rule of 72 is a quick way to figure it out. Related Content A Look at Systematic Withdrawals This calculator may help you estimate how long funds may last given regular withdrawals. The Other Sure Thing Though we don’t like to think about it, all of us will make an exit sometime. Are you prepared? Annuity Comparison This calculator compares a hypothetical fixed annuity with an account where the interest is taxed each year.