Conn. Gen. Stat. § 12-405j

Any taxpayer with respect to a resident estate shall be allowed a credit against the tax otherwise due under this chapter for the amount of any income tax imposed on such estate for the taxable year by another state of the United States or a political subdivision thereof or the District of Columbia on income derived from sources therein and which is also subject to tax under this chapter. The credit provided under this section shall not exceed the proportion of the tax otherwise due under this chapter that the taxable income of such estate, derived from sources in the other taxing jurisdiction, bears to the taxable income of such estate derived from all sources.