26 CFR 20.2053-5: -5 Deductions for charitable, etc., pledges or subscriptions.

(a) A pledge or a subscription, evidenced by a promissory note or otherwise, even though enforceable against the estate, is deductible (subject to any applicable limitations in § 20.2053-1) only to the extent that—

(1) Liability therefor was contracted bona fide and for an adequate and full consideration in cash or its equivalent, or

(2) It would have constituted an allowable deduction under section 2055 (relating to charitable, etc., deductions) if it had been a bequest.

(b) Effective/applicability date. This section applies to the estates of decedents dying on or after October 20, 2009.