They say that quarterly is enough. However, if you don't report an error on your bank/credit card statement within a 60 day window (after getting the statement) you would have missed your boat and will have to "eat" any unauthorized transactions. When it comes to your portfolio (investments under management, 401k, IRA, 403b, TSP, or other) should you give it the same level of attention? After all, you are working very hard to accumulate this money for a comfortable lifestyle at retirement.
Don't feel bad if you haven't been looking at your portfolio for over a quarter. Some people just throw the money in and don't review (forget re-balance) their retirement savings for years. Here are a few reasons for looking at your money more often: 1) markets change, what once was a hot stock or sector no longer is, 2) bonds are not risk free, 3) mutual funds can underperform, 4) there are new investment opportunities each year (for example MLPs).
If you have a difficult time reminding yourself to look at your portfolio you can engage an investment advisor to do it with you. Even if you spend several hundred dollars each quarter (for an hourly fee advisor) you will end up gaining thousands over time in healthy investment portfolio returns. Here is a few hints for your review:
1) If you don’t know how your portfolio performed compared to market or a specific benchmark you haven’t looked at the right performance indicators.
2) If your portfolio is simply following the market you are overpaying for management. If you pay a professional manager to diversify your portfolio they should earn their fees.
3) If your money is in mutual funds, how much do you pay for mutual fund management fees (known as expense ratio, which is money spent on paying the fund's managers and for transactions, if actively trading)? Are the fees higher than 1%? Do you know of less expensive alternatives (ETFs, which usually have lower expense ratios)? If the management fee/expense ratio is 2.5% your money has to make 2.5% to break even forget outperforming the market.