The Supreme court explained at what rate to calculate penalties for late payment of the contract
If the customer has not paid for the goods, works or services in a timely manner, the contractor has the right to charge a penalty for each day of delay. The amount of penalty is 1/300 of the key rate (previously-the refinancing rate).
The Supreme court indicated that the date on which the key rate is set should be determined as follows:
if payment under the contract is made and only penalties are collected, they should be calculated using the rate that was in effect on the date of payment of the debt;
if payment under the contract has not been made, the rate effective on the date of the court decision on debt and penalty shall be applied to the calculation of penalties.
Document: Determination of the Supreme court of the Russian Federation of 18.09.2019 N 308-ES19-8291