The income of a beneficiary of an estate or trust in respect of the estate or trust shall consist of that part of the income or gains received by the estate or trust for its taxable year ending within or with the beneficiary's taxable year which, under the governing instrument and applicable State law, is required to be distributed currently or is in fact paid or credited to the beneficiary. The income or gains of the estate or trust, if any, taxable to the estate or trust shall consist of the income or gains received by it which has not been distributed or credited to its beneficiaries.
61 Pa. Code § 105.2