How Legal Deadlines Are Calculated

Every counting rule answers two things: which day the count starts from, and which days are counted. Neither is obvious, and different rules within the same jurisdiction answer them differently.

Most systems exclude the triggering day and count from the following day, but that is a convention rather than a universal rule. Reading the specific rule is not optional, because the difference is exactly one day and one day is frequently fatal.

A calendar-day period counts every day including weekends and holidays. A business-day period counts only working days, which makes the elapsed time considerably longer for the same number.

Some systems apply different treatment to short and long periods - counting business days for short periods and calendar days for longer ones. Applying the wrong treatment to a short period is one of the more common ways a deadline is miscalculated.

Most systems roll a deadline falling on a weekend or holiday forward to the next working day. Some roll backwards instead, which produces the opposite answer and a shorter period.

Filing methods matter here too. Electronic filing systems often accept documents until late in the evening, while a registry counter closes in the afternoon - and a system outage on the final day is a well-known source of missed deadlines.

Where a period runs from service of a document rather than from an event, the method of service can add days. Postal service commonly attracts additional days that electronic service does not.

Those additions are rule-specific and vary widely. They are also easy to forget, because the underlying period is the number everyone remembers.

Almost every experienced practice diarises a deadline more than once - a working target well before the date, a check point, and the date itself. The purpose is not caution for its own sake.

It is that the work required to meet a deadline is discovered late. A limitation period identified three days before expiry is a period that has effectively already expired, because there is no time to investigate, advise or prepare.

Procedural deadlines can often be extended by agreement or by application. Limitation periods generally cannot, and missing one usually ends the claim regardless of its merits.

They also start from events that are themselves contestable - the date damage occurred, the date it was discoverable, the date a cause of action accrued. Calculating one requires legal analysis, not arithmetic.