"...nineteen per cent of one's capital is payable as Huqúqu'lláh..."

This Law [Huqúqu'lláh] of the Aqdas stipulates that nineteen per cent of one's capital is payable as Huqúqu'lláh when such capital has reached an amount of at least "nineteen mithqáls in gold".... In determining the amount a believer should pay, he should first deduct any debts and expenses he may have, and pay nineteen per cent of the remainder of his capital if it is equal to at least nineteen mithqáls of gold. 

- The Universal House of Justice  (From a letter dated 21 January 1973; The Compilation of Compilations, vol. I, Huququ’llah)