Getting multiple error results in a column called "Birthdate" in Power Query (From a CSV) when I try to change the Column type from "Text" to "Date".

Convert Birthdate with Change Type → Using Locale → Date → English (United States) so Power Query interprets 8/26/1961 as month/day/year rather than using the Indian system locale.

Convert the column in Power Query

1. In Applied Steps, delete the existing Changed Type step that produced the errors.
   • If that step also converted other columns, select its gear icon and remove only the Birthdate conversion, or recreate those other conversions afterward.
2. Right-click the Birthdate column heading.
3. Select Change Type → Using Locale.
4. In Change Column Type with Locale, choose:
   • Data Type: Date
   • Locale: English (United States)
5. Select OK.

Power Query Desktop normally uses the operating-system regional format when interpreting text. Using Locale overrides that behavior for this conversion, which is appropriate when a CSV uses a different date convention.^1^

8/26/1961 should now become a genuine date value representing 26 August 1961. The way it is subsequently displayed can follow workbook or regional formatting; the underlying year, month, and day remain the converted date components.

Equivalent M code

The UI operation normally creates a culture-explicit step like this:

let
    PreviousStep = #"Promoted Headers",
    ConvertedBirthdate =
        Table.TransformColumnTypes(
            PreviousStep,
            {{"Birthdate", type date}},
            "en-US"
        )
in
    ConvertedBirthdate

Replace #"Promoted Headers" with the actual preceding step name in the query. Table.TransformColumnTypes accepts an optional culture such as "en-US" for type conversion.^2^

For a conversion that explicitly declares the expected text pattern, use Date.FromText:

let
    PreviousStep = #"Promoted Headers",
    ConvertedBirthdate =
        Table.TransformColumns(
            PreviousStep,
            {{"Birthdate",
              each Date.FromText(_, [Format="M/d/yyyy", Culture="en-US"]),
              type date}}
        )
in
    ConvertedBirthdate

Date.FromText supports both Format and Culture options.^3^ Use this version only if the CSV consistently uses slash-separated US dates such as 8/26/1961.

Verify the result

To verify that ambiguous values such as 1/2/1961 were interpreted correctly:

1. Select the converted Birthdate column.
2. Open Add Column.
3. Use the Date commands to extract Day, Month, and Year into temporary columns.
4. Confirm that the source value 8/26/1961 produces:
   • Month: 8
   • Day: 26
   • Year: 1961
5. Remove the temporary verification columns.

If errors remain after the locale-aware conversion, inspect only those rows. They likely do not conform to the selected US date convention—for example, blank-like text, malformed values, or another date pattern—and should not be silently converted until their actual source format is identified.

Changing the workbook-wide regional setting is unnecessary for this column. If all imported data in the workbook uses US conventions, the broader setting is available at Power Query Editor → File → Options and settings → Query options → Current Workbook → Regional Settings, but the per-column Using Locale conversion is safer when only this CSV requires US parsing.^4^

References

1. Data types in Power Query
2. Table.TransformColumnTypes
3. Date.FromText
4. How culture affects text formatting