You must choose what to pack inside it—stocks, bonds, cash—or else the firm that handles your account will choose for you (if that ends up being a cash account, you'll miss out on the opportunity to earn bigger returns by putting at least a portion of that money in stocks).
There is no "best" retirement investment.
What's right for you and for your closest friend can be wildly different, depending on a variety of factors: your age, whether you will have other retirement income sources (Social Security, a pension, an inheritance), your appetite for risk. If you invest through an employer-provided plan, look for educational material on the company Web site to help you choose the right mix. If you're investing on your own, consider consulting a trusted financial adviser. Overall, I recommend subtracting your age from 100 and putting that percentage in stocks (so if you're 30, that means 70 percent).
Diversification is key.
When you invest through a retirement plan at work, you're usually offered a menu of mutual funds, which provide a basket of investments in one shot. With your own IRA, you can also build a diversified portfolio by opting for low-cost exchange-traded funds (ETFs): Each fund holds dozens if not hundreds of investments.
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