How often should you update your will?

If your worldly possessions included a Betamax and an 8-track tape player the last time you looked at your will, it might be time for a reassessment.

Legal experts estimate the average will has not been updated in 20 years. Many people wait until a cataclysmic event, such as the death of a spouse, before updating their will. But over the course of two decades, even small changes in your circumstances can combine to make your will either outdated or one that no longer reflects your wishes.

The American Bar Association, in its "Guide to Wills and Estates," lists several occurrences that should trigger a will re-evaluation. In addition to the death of a spouse, major events include divorce or the death of named beneficiaries. You also may have had more children or grandchildren that you want to name specifically. And don't forget the executor. The person you named years ago to handle your affairs may have died or is no longer suitable. (To see the entire ABA estate plan checklist, go to bit.ly/wills-aba.)

Even in the absence of any of these life-changing events, keep in mind tax laws change almost every year. What was a good estate plan in 1991 may have negative consequences for your heirs in 2011. Additionally, many people have living arrangements that include a significant other but not a spouse.

"We all think in terms of the traditional: 'I leave everything to my wife, and if my wife's not around, I leave everything to my kids,' " says Jules Haas, a Manhattan-based lawyer specializing in estate planning. "But many people don't have the traditional wife and they don't have children."

For example, some widowed or divorced older folks pair up but do not get married. Haas points out that a partner not named in the will may receive nothing because he or she does not have spousal rights.

And especially in the case of a nasty divorce, Haas says remember to change beneficiary designations on retirement funds, life insurance policies and bank accounts. These assets, when a beneficiary is named, are not controlled by the will. If your ex-spouse is listed as the beneficiary, he or she will almost certainly get those assets if you die.