WhenMathInclusive vs Exclusive Date Counter
The same two dates can produce four different day counts depending on whether each endpoint is included. See all four at once so you can pick the one that actually matches your question.
Worked example
From January 1 to January 31, the four conventions give four different answers: excluding both dates counts 29 days between them; including start but excluding end (or the reverse) both count 30; including both dates counts 31. A notice period that says "30 days" almost always means one of the middle two, not the 29- or 31-day extremes, but the exact convention should always be confirmed against its actual source.
Limitations
This shows all four counting conventions for information; it does not determine which one a specific contract, law, or policy actually uses.
Frequently asked questions
- Which convention does WhenMath use by default elsewhere?
- Exclude start, include end, unless a specific engine states otherwise; see the Methodology page.