My son is a full time law student in CO, AZ resident. He had a small paid internship this summer and paid fed/CO taxes on the income. Do we need to file both AZ and CO?

[DanielV01 · Accepted solution]

Probably.  If his internship is taxable in Colorado, and he has enough taxable income to have a filing requirement in both Colorado and Arizona, he would file tax returns to both.  Colorado may tax the internship (if it is taxable income in Colorado) as a nonresident, and Arizona would tax all of his income as a resident.  In this case, Arizona will give him a credit for the tax he pays to Colorado on the income he earns there.