The tax due on Form 2438, Undistributed Capital Gains Tax Return, is the tax on the capital gains that have not been distributed to the taxpayer. The tax payment is typically made with the filing of the form. The due date for filing and paying the tax depends on the taxpayer's tax year. For most taxpayers, the due date is April 15, but it may be later if this date falls on a weekend or holiday. Extensions to file and pay may be available. It is important to note that the tax payment is separate from any estimated tax payments that may be required throughout the year.