Millions of American taxpayers are much more generous than they realize -- or intend to be.

Each year, many people overpay their taxes by neglecting to take advantage of deductions, credits and other breaks. Some commonly overlooked items, such as a one-time credit for the 2006 tax year for taxes paid on certain phone services, are relatively simple. Others, such as a recently enacted exclusion for mortgage-debt forgiveness, are easier to miss because they're new and can be tricky.

Welcome to what might be labeled "complexity taxes" -- additional taxes that people wind up paying because they don't have the time, knowledge, energy or patience to master the increasingly complex Internal Revenue Code.

If you neglected to claim an important break on a return in a recent year, don't compound your error by automatically assuming it's too late to correct the situation. Just file what's known as an amended return. Use Form 1040X, available on the Internal Revenue Service Web site (www.irs.gov). Generally, you have to file your claim for a credit or refund within three years of the date you filed your original return, or within two years of the date you paid the tax, whichever is later, according to the IRS.