The Kitab-i-Aqdas, Baha'u'llah's book of laws revealed in 1873, establishes Huquq'llah, literally the Right of God, as an obligation distinct from every other financial instruction in Baha'i scripture. Once a believer's wealth, after essential living and business expenses, exceeds a fixed threshold set in the original unit of value named in the text, nineteen percent of the surplus becomes due, and it becomes due again on any further increase above that threshold, a marginal rather than a repeating flat calculation. Baha'u'llah reserved administration of the fund to himself during his lifetime and, in the Aqdas and in his will, passed that authority first to Abdu'l-Baha, then through the line of succession to Shoghi Effendi as Guardian, and since 1963 to the Universal House of Justice, which today directs Huquq'llah's collection and disbursement through appointed trustees.
No external body audits or enforces individual payment; the calculation, the honesty of the accounting and the decision to pay at all rest entirely with the believer, and Baha'i teaching treats this as intentional rather than an administrative gap. Abdu'l-Baha and Shoghi Effendi's writings describe Huquq'llah as a test of a believer's detachment from wealth and sincerity of faith precisely because it cannot be compelled, framing it as much as a spiritual practice as a fiscal one, comparable in that respect to the Nineteen-Day Fast's emphasis on inward disposition over outward observance.