Date.StartOfDay

Date

Returns the first moment of the day (midnight) for the given date or datetime value.

Syntax

Date.StartOfDay(dateTime as any) as any

Parameters

Name	Type	Required	Description
`dateTime`	`any`	Yes	A date, datetime, or datetimezone value.

Return Value

any — A datetime or datetimezone value representing 00:00:00 on the given day.

Remarks

Date.StartOfDay returns the very first instant of the day — 00:00:00 — as a datetime. When passed a plain date, it returns a datetime with the time component set to midnight. When passed a datetimezone, it preserves the timezone offset and sets only the time components to midnight. This is useful for building inclusive lower-bound date range filters.

A common pattern is combining Date.StartOfDay and Date.EndOfDay to create an inclusive day range: [EventTime] >= Date.StartOfDay(start) and [EventTime] <= Date.EndOfDay(end). This avoids filtering bugs that arise from comparing a datetime column against a bare date value.

Note that Date.StartOfDay applied to a datetime truncates to midnight of that datetime's day. If the input is already 00:00:00, the output is unchanged. To truncate a datetime to a specific hour instead of midnight, use Time.StartOfHour.

Examples

Example 1: Filter log entries on or after the start of a specific day

Table.SelectRows(
    OrderLog,
    each [Timestamp] >= Date.StartOfDay(#date(2024, 1, 16))
)

Result

	LogID	OrderID	Action	Timestamp	DurationMinutes	Notes
1	L002	1	Shipped	1/16/2024 2:15:00 PM	1,725	Shipped via express
2	L003	2	Created	1/18/2024 11:00:00 AM	null	New order: Gadget B
3	L004	2	Shipped	1/20/2024 8:45:00 AM	2,745	Standard shipping
4	L005	3	Created	2/1/2024 4:20:00 PM	null	New order: Widget C
5	L006	3	Cancelled	2/2/2024 10:05:00 AM	1,065	Customer request
6	L007	4	Created	2/10/2024 1:00:00 PM	null	New order: Gadget D
7	L008	4	Shipped	2/12/2024 9:30:00 AM	2,670	Shipped via express

Example 2: Return the start-of-day datetime for March 15, 2024

#table(
    type table [Result = datetime],
    {{Date.StartOfDay(#date(2024, 3, 15))}}
)

Result

	Result
1	3/15/2024 12:00:00 AM

Example 3: Build an inclusive date range filter using StartOfDay and EndOfDay

let
    TargetDate = #date(2024, 1, 15),
    RangeStart = Date.StartOfDay(TargetDate),
    RangeEnd = Date.EndOfDay(TargetDate)
in
    Table.SelectRows(
        OrderLog,
        each [Timestamp] >= RangeStart and [Timestamp] <= RangeEnd
    )

Applied Steps

The final output — filters the OrderLog table to rows whose Timestamp falls on January 15, 2024.

	LogID	OrderID	Action	Timestamp	DurationMinutes	Notes
1	L001	1	Created	1/15/2024 9:30:00 AM	null	New order: Widget A

Compatibility

✓ Power BI Desktop✓ Power BI Service✓ Excel Desktop✓ Excel Online✓ Dataflows✓ Fabric Notebooks