To illustrate the increased earnings capacity of tax-deferred interest, compare it to a fully-taxable earnings. $25,000 at 6.0% will earn $1,500 of interest in a year. A 28% tax bracket means that approximately $420 of those earnings will be lost in taxes, leaving only $1,080 to compound the next year. If these same earnings were tax-deferred, the full $1,500 would be available to earn even more interest. The longer you can postpone taxes, the greater the gain.