As I was planning my 401k, I happened across Morningstar's Instant X-Ray. You enter the ticker symbols (mutual funds, ETFs, and stocks are all good here) and it will tell you how your portfolio is weighted. It took me about an hour to get my portfolio weighed right, but it was really time well spent.
I found a combination of 6 mutual funds that gives me a near 70% US stock, 30% foreign stock mix. I can't use this money for 30 years, so I'm fine with betting on the foreign markets. My style diversification box (the famous Morningstar 9 box grid) has no more than 13% and no less than 10% in any area. This means that I'm very close to being equally weighted in small, mid, and large companies, as well as those that are value, core, and growth.
I've got 15% in Information sectors (which is great because I work in that sector and don't want to overweigh it), 52% Services (a little high, but the S&P is waited at 47%, so it's not that far off), and 33% Manufacturing. My average expense ratio is a miserly 0.87% as I took good care to not add funds that have high expense ratios. I couldn't believe that one fund choice available to me had an expense ratio over 2% - Yikes! Lastly, my foreign exposure is 16% Europe, 5% Japan, 3% Latin America, and 3% Pacific Rim.
Best of all, I actually found it fun to play with the stock and the percentages. This weekend, I will probably extend this to my whole portfolio. The basic tool is free, but if you pay you get a lot of extra features.
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