Inclusive vs Exclusive Date Counter

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 conventions, not the 29- or 31-day extremes, but the exact convention should always be confirmed against its actual source rather than assumed from the wording alone.

Common mistakes

• Assuming "30 days" and "days between the two dates" always mean the same count. Depending on which endpoints are included, the same two calendar dates can produce four different numbers, and only one of them is likely to match the source's intent.
• Applying one convention consistently across a whole contract or policy without checking that every clause actually uses the same rule. A notice period and a billing period in the same document do not always share a counting convention.

Limitations

This shows all four counting conventions for information. It does not determine which one a specific contract, law, or policy actually uses, so the underlying source document should be checked to confirm which of the four answers actually applies.