Principles of International Commercial Contracts, 1994 - UNIDROIT
Chapter 7 - Non-Performance
Section 4 - Damages
Article 7.4.9 - Interest for Failure to Pay Money
(1) If a party does not pay a sum of money when it falls due the aggrieved party is entitled to interest upon that sum from the time when payment is due to the time of payment whether or not the non- payment is excused.
(2) The rate of interest shall be the average bank short-term lending rate to prime borrowers prevailing for the currency of payment at the place for payment, or where no such rate exists at that place, then the same rate in the State of the currency of payment. In the absence of such a rate at either place the rate of interest shall l be the appropriate rate fixed by the law of the State of the currency of payment.
(3) The aggrieved party is entitled to additional damages if the non-payment caused it a greater harm.