Don't Let Models Calculate Dates Themselves
kumard3 · reddit · 2026-07-14
The author points out that current frontier models still get the day of the week wrong by a day or two when handling relative dates. For example, terms like "next Wednesday" or "Tuesday in two weeks" show a non-trivial frequency of errors in production environments.
The proposed solution is to remove date reasoning from the model's responsibilities: first, inject a date-week mapping table for the upcoming weeks into the system prompt for direct lookup; second, provide a deterministic resolvedate tool, and let the server, not the model's parameters, provide currentdate and timezone.
The core principle is that any deterministic task prone to model errors should be handled by ground truth or tools, with date calculation being the classic example.
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