Shifting markets can throw an investor’s mix of stocks, bonds and other assets off-target. For example, if stocks rally, a portfolio with 60 percent in stocks and 40 percent in bonds may grow to 70 percent in stocks. This means the investor is taking on more risk than intended. It’s possible to get back on track by rebalancing the portfolio to restore the desired asset allocation. Here’s a look at some tools to help determine an ideal mix for you, and stick with it:

—CHOOSING A PLAN: Most major investment companies offer guidance on their Web sites on how to choose an appropriate asset allocation, and how to shift it as you approach retirement. Financial planners also can help. The U.S. Securities and Exchange Commission offers tips at http://www.sec.gov/investor/pubs/assetallocation.htm

—STICKING WITH THE PLAN:

— Morningstar’s Web site offers a tool called Instant X-Ray to uncover strengths or weaknesses in a portfolio, including its mix of assets and exposure to different types of stocks. More in-depth analysis is available using a version called Portfolio X-Ray, available to paid Premium Morningstar members. For example, you can plug in totals for a variety of savings accounts, such as 401(k)s and IRAs, to get an overall picture of your portfolio.

— Another Morningstar tool called Portfolio Monitor delivers analyst research on your portfolio’s top holdings, and gives you hypothetical outlooks on your portfolio’s potential value in the future, ranging from five to 30 years. Regular e-mails provide portfolio performance updates, and breakdowns of your holdings.

— A tool at http://www.assetplay.net/financial-tools/rebalance.html helps calculate how many shares of an investment to buy when rebalancing.

— Other rebalancing tools are at: http://www.invest-it-yourself.com/rebalancing.php

—MAKE IT AUTOMATIC: Many mutual fund companies and workplace savings plans offer target-date mutual funds, or lifecycle funds. These products help investors saving for retirement by automatically shifting to a more conservative asset mix the closer you get to retirement — a decent option for those unlikely to rebalance their portfolio on their own. But you’ll still need to monitor their performance — there are no guarantees.