Nonprofit organizations are subject to an Unrelated Business Income Tax (UBIT) on activities unrelated to their tax exempt purpose. In 2007 nonprofits became the first U.S. federal taxpayers required to publicly disclose their income tax returns. Using this data I find that nonprofits avoid the UBIT by combining losses from some activities to offset the profits of other activities. A provision in the Tax Cut and Jobs Act of 2018 was effective in mitigating the use of loss activities as a UBIT avoidance method. I also find that nonprofits continue to avoid the UBIT by shifting common costs from tax exempt to taxable activities. I find that UBIT avoidance is increasing in tax rates. Finally, tax avoidance is smaller for the set of nonprofits organized as charitable trusts rather than as corporations or associations, and that public donors play a governing role by mitigating UBIT avoidance. Data Availability: Data are available from sources identified in the text. JEL Classifications: H26; L30.