# What is the Base Date Index?

**URL:** <https://reachback.builtintelligence.com/t/what-is-the-base-date-index/852>\
**Category:** Secondary X, W and Y options\
**Created:** [16 October 2012 11:23 UTC](https://reachback.builtintelligence.com/t/what-is-the-base-date-index/852 "2012-10-16T11:23:40Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![BuiltIntelligence](https://avatars.discourse-cdn.com/v4/letter/b/919ad9/32.png) [@BuiltIntelligence](https://reachback.builtintelligence.com/u/BuiltIntelligence)\
**Post date:** [16 October 2012 11:23 UTC](https://reachback.builtintelligence.com/t/what-is-the-base-date-index/852/1 "2012-10-16T11:23:40Z")

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What is the Base Date Index?

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**Author:** ![BuiltIntelligence](https://avatars.discourse-cdn.com/v4/letter/b/919ad9/32.png) [@BuiltIntelligence](https://reachback.builtintelligence.com/u/BuiltIntelligence)\
**Post date:** [16 October 2012 11:23 UTC](https://reachback.builtintelligence.com/t/what-is-the-base-date-index/852/2 "2012-10-16T11:23:54Z")

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The Base Date Index (B) is the latest available date before the base date (see Clause X1.1(a)).