Their income taxes must be paid into the Treasury of Guam. Non-residents except those who acquired their U.S. citizenship through the Organic Act, or through naturalization proceedings in the District Court of Guam, incur income tax liability to Guam only on income derived from Guam sources. Self-employed individuals who are covered by the Federal Old Age Insurance and Schedule C of individual income tax return Form 1040. In such case the U.S. Internal Revenue Code provides that no return need be filed with the U.S. Internal Revenue Service. Guam individual tax rates are the same as those in the U.S. Internal Revenue Code and can be found in Section 1 of the Guam Territorial Income Tax Law.
Guam corporations are subject to income tax on their income from all sources.
Other corporations doing business on Guam incur income tax liabilities to Guam on all Guam source income. The tax rates for corporations doing business on Guam can be found in Section 11 of the Guam Territorial Income Tax Law. Individual income tax returns for the calendar year are due on or before April 15 of the following year. Individuals reporting on a fiscal year basis must file their returns on the 15th day of the fourth month following the close of the fiscal year. Corporations are required to file an income tax return for the calendar year on or before March 15 of the following year.