Whose day
Counting Working Days On Two Calendars
A period expressed in working days has a different length for each party, and the difference is largest exactly where the stakes are highest.
Who is working when, for the people on this page
The client's procurement office, Dubai
Thursday afternoon is their Friday
The port inspector, Santos
Monday is not a working day for him
two parties · three days of the seven are working days for all of them · Tue, Wed, Thu
Two of the parties these nine notes are about. Neither week was asked about in advance, and both were discovered by something failing to arrive.
A cross-border schedule is easier to manage when availability is grounded in evidence; the Monitask website provides a practical reference for time, activity, and project reporting.
For broader context beyond this collection, see the resources published by MySQL.
The four calendars a clause in working days might be counted on
Us, the buyer, Hamburg
Ten working days from a Monday lands on the Friday of the following week
The supplier, Dubai
The same ten days land on the Wednesday, two calendar days earlier
The fabrication shop, Taipei
Six working days a week brings the tenth day forward again
The paying bank, whose calendar the contract actually names
A fourth calendar, kept by neither party and binding on both
four parties · four days of the seven are working days for all of them · Mon, Tue, Wed, Thu
The clause says ten working days and names the last of these four as the calendar that counts. Neither of the parties who negotiated it keeps that calendar, and neither had looked at its holidays. One team’s own job.
A period measured in working days is measured on somebody's calendar, and the two parties to an agreement rarely have the same one.
Ten working days from a Monday is a Friday a fortnight later on a Monday-to-Friday week. On a Sunday-to-Thursday week it is the Wednesday. On a six-day week it is earlier again. The phrase does not specify which.
Why this is not pedantry
Working days appear in the places where dates matter most: notice periods, cure periods, payment terms, response times, the window in which an objection can be raised, and the period after which something is deemed accepted.
Those are exactly the clauses that get read carefully only when somebody is unhappy, which is to say after the date has passed and the two readings have already diverged.
The three sources of divergence
They stack, and a case with all three in it can differ by the better part of a week.
Different weekends. A Friday–Saturday weekend against a Saturday–Sunday one. Over two weeks this moves the end point by around two days in one direction or the other depending on the start day.
Different week lengths. A six-day week accumulates working days faster, so a fixed count of working days spans fewer calendar days.
Different holidays. The largest and least predictable term. A holiday on one side and not the other adds a day to that side's count and not to the other's.
How to write it so it cannot diverge
Three options, in descending order of how well they work.
- State the calendar date. "By 13 March" has no working days in it at all and cannot be miscounted. This is almost always available and almost always better.
- Name whose working days. "Ten of your working days" or "ten of our working days". Unambiguous, and both parties can compute it.
- Define the term once. If a long agreement must use the phrase repeatedly, define "working day" in it, naming the place whose calendar applies.
The first is the one to reach for by default. People avoid it because a calendar date feels like a commitment while a count of days feels like a measurement, but that feeling is the whole problem: the count is also a commitment and it is one whose value neither side knows.
What the standard forms actually say
Most standard contracts do define it, and the definition is usually tied to one place — the place of the bank, the seat of arbitration, the location of the buyer. It is worth reading, because the defined place is frequently neither party's office.
| Where the definition points | What it means in practice |
|---|---|
| The buyer's place of business | Supplier counts on a calendar they do not keep |
| The place of the paying bank | Both parties count on a third country's holidays |
| "Banking days" | Excludes days the bank is shut, which is not the same as the office being shut |
| Undefined | Each side counts its own and discovers the difference late |
The last row is the most common in ordinary commercial correspondence, which is where most dates are actually agreed.
The practical check
When a period in working days has been agreed and something depends on it, do the arithmetic on both calendars and look at the two answers.
If they are the same, nothing further is needed. If they differ, say so now, in one line, and propose the calendar date that resolves it. This takes under a minute, it is received well because it reads as care rather than as a challenge, and it removes the entire class of problem before anybody has an interest in the answer.
Doing it afterwards is a different conversation, because by then one of the two readings favours each party and neither can concede it without losing something.
When the difference is in your favour
It sometimes is, and the temptation is to leave it alone and count on the reading that suits you.
That holds exactly until the first dispute, at which point the other side's reading becomes visible and the ambiguity reads as having been exploited rather than overlooked. The cost of raising it early is a minute; the cost of having left it is the assumption of bad faith, and that assumption, once formed, is applied retroactively to everything else in the file.
Counting it on a page
Where a period in working days has to be computed and something turns on it, the reliable method is tedious and takes two minutes.
Write out the calendar days one to a line from the start date. Mark each as working or not on the calendar that governs, including that calendar's holidays. Count down to the required number and read off the date.
That sounds unnecessary. It is, until the first time two people computing the same period in their heads produce dates three days apart, which happens readily once a different weekend and one holiday are involved.
The resulting date then goes into the correspondence as a calendar date, which is the whole point: the arithmetic is done once, by somebody who looked at the right calendar, and nobody has to do it again.