A supplemental needs trust is an important tool that can be used to make sure a child with special needs has access to the services and care he or she requires. Establishing a supplemental needs trust as a part of an overall financial plan is one step in providing a solid base of lifetime support. Once a child turns 18, his or her income will be used to determine eligibility for public benefits such as Medicaid and Supplemental Security Income (SSI). Earning too much will lead to the loss of these important benefits. However, funds paid into a supplemental needs trust will not be counted as income and, therefore, will allow an individual with special needs to retain public benefits.