The general rule for calculating a period of time under most arbitration rules is that the period shall begin to run on the day following the day when a notice is received. If the last day of such period is an official holiday or a non-business day at the residence or place of business of the addressee, the period is extended until the first business day which follows. Official holidays or nonbusiness days occurring during the running of the period of time are included in calculating the period.
From this statement we can derive three main variables. (1) The day when the time count begins to run; (2) the period that it encompasses and (3) the last day of the period. The formula Z-C-B (Zero-Calendar-Business) encompasses the three variables and will be helpful for time calculations.
The first element Z (ZERO)
Article 2 of the UNCITRAL Arbitration Rules (2021) is clear in that the period shall begin to run on the day following the day when a notice is received. Similarly, article 3.4 of the ICC Arbitration Rules (2021) states that the time shall start to run on the day following the date of notification or communication is deemed to have been made. Article 4.6 of the LCIA Rules (2020) provide that the period shall begin to run on the day following the day when a written communication is received by the addressee. Rule 5 of the SIAC Arbitration Rules (2025) considers that the period shall commence from the day following the receipt of a written communication or a deemed receipt of such written communication.
The common trait is that the count begins from “the following day”. Hence, we can derive that the day a notice is received or a written communication is received can be considered as “day zero”, in order to begin counting “day one” on the following day. We can mentally represent this as follows:
Wednesday June 8th (Day 0) – Thursday June 9th (Day 1)
However, please note that the ICC Arbitration Rule differs from others and specifies that when the day next following such date is an official holiday, or a non-business day in the country where the notification or communication is deemed to have been made, the period of time shall commence on the first following business day, in which case, considering an hypothetical scenario in which June 9th was an official holiday, the rule would apply as follows:
Wednesday June 8th (Day 0) – Thursday June 9th (Day 0) – Friday June 10th (Day 1).
The second element C (CALENDAR)
This second element represents all the time period that is encompassed between the first day and the last day, with reference to the place of receipt of the communications. In this regard Article 2 of the UNCITRAL Arbitration Rules (2021) clarifies that official holidays or nonbusiness days occurring during the running of the period of time are included in calculating the period. The same occurs under the ICC Arbitration Rules, LCIA Arbitration Rules and SIAC Arbitration Rules.
The C in the formula, thus, represents that all the time period between the first and the last day should be calculated in calendar days. All official holidays and nonbusiness days would naturally count.
The third element B (BUSINESS)
The last element regards the last day of the period with respect of the place of the receipt of the communication, the pace of the addressee or the place of the party against whom the calculation of time applies. ICC Arbitration Rules state that if the last day of the relevant period of time granted is an official holiday or a non-business day in the country where the notification or communication is deemed to have been made, the period of time shall expire at the end of the first following business day. LCIA Arbitration Rules and SIAC Arbitration Rules both provide for an extension until the first business days which follow the last day of the period when the last day happens to be a statutory holiday or non-business day.
This situation can be summarized by saying that, no matter what happens, the last day of the period has to be a business day. Thus, it is represented in the formula with the “B” of business day. Regardless of whether we extend the period of time for Saturday, for Sunday or for an official holiday, we should bear in mind that the last day cannot be a non-business day.
In conclusion
The rule Z-C-B (zero, Calendar, Business) is a mnemotechnic aid for practitioners to remember that the day in which a communication is received will be considered “Day Zero”, the count begins the following day, including all Calendar days until, at the end, we land on a Business day. Albeit this general rule, attention should be drawn for any exceptions or modifications due to rule amendments, party’s agreement or Arbitral Tribunals´ order.
