Of course, saving 15 percent of your pre-tax income when you're 25 is not easy. Young adults are typically just getting going in their careers -- with salaries to match. They might have student loans to pay off. And some young people simply find it difficult to put money away for a goal like retirement that seems impossibly far into the future. But the numbers don't lie: Retirement is a hugely expensive challenge, and the earlier you start investing for it, the better.
The easiest way to save is to arrange an automatic transfer to your savings or investment account each month; that way, you won't have to consciously make the "save or spend" decision each month. A payroll deduction plan is ideal, especially if it goes into a tax-advantaged plan like a 401(k) or an IRA account. Your 401(k) plan contributions are often matched to some degree by your employer, which makes your effective savings rate even higher.
These guidelines should put you in good shape for retirement, but people have plenty of other savings goals, too:
-- Emergency fund: If you don't have a cash cushion, another goal should be to put away three to six months worth of cash in something very liquid and very safe just in case something unforeseen happens.
-- A child's education: If you have kids, saving for college is an excellent idea -- the earlier the better. Use a 529 plan to shelter investment gains and income from taxes. The amount you need to save will depend on your income and the type of college (public or private) you envision.
-- The down payment on a house: A more near-term goal for many people is buying a home of their own. If you've started saving for retirement and you've built an emergency fund, you'll probably just want to save as much as you can afford (on top of saving for your retirement and other goals) to buy your own home.
To recap: Let your goals determine your savings habits. Most of us have multiple savings "buckets," with retirement being the highest priority.
Finally, remember that "saving" in today's world really means investing. For longer-term goals, you'll likely need to tap the potential of the financial markets (particularly the equity markets) to give your savings the chance to grow into wealth. Best of luck!