Today's AI Tip
Asking AI for a business-day deadline? Make it list each day.
The quick answer hides its count
Real output · GPT-5.5 (OpenAI API) · Oct 2026
We asked for the deadline 15 business days after Monday, Nov 2, 2026, with the office closed on US federal holidays, and said to just give the date. Both runs gave a date and no counting rule.
Add one line that makes it show work
Tested in GPT-5.5 (OpenAI API), Oct 2026
Put this after your deadline question. It asks the AI to number every business day it counts and to name each day it skips.
Try it: paste this line under your next deadline question.
Now the assumption is on the page
Real output · GPT-5.5 (OpenAI API) · Oct 2026
The list gave the same date, Nov 24, but it also said that Nov 2 was not counted, skipped Veterans Day, and named the other rule.
Our own recount matches the list
We recounted on a calendar, skipping weekends and Veterans Day on Nov 11, and day 15 landed on Tuesday, Nov 24. The quick answer was right, but it never said how it counted.
Source: OPM Federal Holidays (2026); our calendar recount
Is today day 1?
That one choice moves the date by a day: skipping Nov 2 gives Nov 24, and counting it gives Nov 23. Federal court rules exclude the trigger day, but your contract may say otherwise.
Source: FRCP Rule 6(a)(1), Cornell LII
The list can't settle it for you
The list shows the assumption but can't decide it. One run called skipping today "the usual counting convention." If your office keeps other holidays, or works Veterans Day, say so. The contract decides.
Check day 1 and the skipped days
Paste the list line under any deadline question. Then check day 1 and the skipped days against your contract and calendar, and put the date in your diary.
Try it: ask for your next notice or invoice deadline.
Sources and assumptions
- U.S. Office of Personnel Management, Federal Holidays (2026): Veterans Day 2026 is Wednesday, November 11; Thanksgiving is Thursday, November 26 (after the deadline window) (checked 2026-10-19)
- Federal Rules of Civil Procedure Rule 6(a)(1), Legal Information Institute (Cornell Law School): Courts' time-computation rule says to 'exclude the day of the event that triggers the period'. It is an example of the trigger-day convention only: FRCP 6(a)(1) counts calendar days and governs court deadlines, not contracts (checked 2026-10-19)
- Our own calendar recount (Python datetime), 2026-10-19: Nov 2, 2026 is a Monday; counting 15 weekdays from Nov 3 while skipping Nov 11 lands on Tuesday, Nov 24, 2026; counting Nov 2 as day 1 lands on Monday, Nov 23 (checked 2026-10-19)
- Anthropic, Prompting best practices: Long context prompting (checked while researching the rejected idea): Not used on slides. Backs only the rejection of i-2026-10-18-02: the tip applies to '20k+ tokens' inputs, and 'Queries at the end can improve response quality by up to 30 percent in tests' (checked 2026-10-19)
Assumptions:
- The scenario is fictional: a supplier contract with a 15-business-day written-notice period, triggered on Monday, Nov 2, 2026.
- The office is closed on US federal holidays (as the prompt says), so Veterans Day (Nov 11) is skipped. Many private businesses stay open that day, which would move the date earlier.
- The deadline of Nov 24 assumes the trigger day (Nov 2) is not counted. Counting it as day 1 gives Nov 23. A real contract's definitions decide which rule applies.
- The tests ran in GPT-5.5 through the OpenAI API (label: 'GPT-5.5 (OpenAI API)'), not the ChatGPT app or Claude. The Claude test runner failed in this research session, so no Claude result exists and none may be claimed.
- Time of day, time zones and mail or delivery rules for 'sending' notice are out of scope.
The short version
- A quick date can hide its counting rule.
- Ask for a numbered list of each day.
- Check day 1 and the skipped days.
- Your contract decides, not the AI.
