The power can be exercised only in favour of a beneficiary who has an interest in capital (which may be a contingent or remainder interest) and not, for example, in favour of a beneficiary who can only benefit if the trustees exercise a discretionary power.

For trusts created before 1 October 2014, it applies only to half of a beneficiary's interest in the trust fund. Most modern trust documents extend the power to apply to the whole of a beneficiary's share, but older trust documents and simple will trusts often do not. This restriction has been removed by section 8 of the Inheritance and Trustees' Powers Act 2014 for trusts and will trusts created or arising on or after 1 October 2014.

Any beneficiary with a prior interest (such as a life tenant) must consent to the exercise of the power.

Advances must be taken into account when the beneficiaries who receive them later become entitled to capital.