# Birthday day derivation

Indicates how the day of birth was sourced (e.g., declared, modeled, or imputed at household level).

- API name: `birthday_day_derivation`
- Category: Life event
- Type · unit: Text
- Individuals with a value: 235.1M (91.3%)
- Latest collection: Jun 1, 2026, refreshed every two months
- How values combine: Read from a single source field.

## Links

- [Catalog page](/catalog/v2/birthday_day_derivation)
- [Published statistics (JSON)](https://static.faraday.ai/figv2/birthday_day_derivation.json)
- [API reference](/docs/reference/getattribute)