Compound interest is an extremely powerful force that allows you to earn exponentially larger gains on your money over time — so the money you save now is worth a lot more than the money you save later. Here’s a simple example: You invest $1,000 today and earn an annual 5% gain, so $50. That $50 is added to the principal amount of your investment, and then next year, you earn a 5% gain on $1,050, so you earn $102.50. And so on… So, the earlier you start saving, the more your money will grow over time!
Source : http://www.ajc.com/business/personal-finance/saving-101-why-you-should-save-and-how-get-started/c5Ywg3UyUbtxgTvnOX8ghJ/