Soenneker.Extensions.DateTimeOffsets.Days

Computes current, previous, and next day boundaries for DateTimeOffset, either in its stored offset or in a named time zone with UTC results.

Installation

dotnet add package Soenneker.Extensions.DateTimeOffsets.Days

Boundaries in the stored offset

using Soenneker.Extensions.DateTimeOffsets.Days;

DateTimeOffset value = new(2026, 8, 29, 16, 42, 30, TimeSpan.FromHours(-4));

DateTimeOffset start = value.ToStartOfDay();
DateTimeOffset end = value.ToEndOfDay();
DateTimeOffset previousStart = value.ToStartOfPreviousDay();
DateTimeOffset nextEnd = value.ToEndOfNextDay();

Method	Result
ToStartOfDay()	Midnight on the stored calendar date
ToEndOfDay()	One tick before the next stored date
ToStartOfPreviousDay()	Midnight on the previous stored date
ToEndOfPreviousDay()	One tick before the current stored date
ToStartOfNextDay()	Midnight on the next stored date
ToEndOfNextDay()	One tick before the date after next

These methods preserve the value's offset and use calendar arithmetic on its existing fields. They do not consult a TimeZoneInfo, so that fixed offset does not automatically change across DST.

Boundaries in a named time zone

TimeZoneInfo eastern = TimeZoneInfo.FindSystemTimeZoneById("America/New_York");
DateTimeOffset instant = new(2026, 8, 29, 18, 0, 0, TimeSpan.Zero);

DateTimeOffset localDayStartUtc = instant.ToStartOfTzDay(eastern);
DateTimeOffset localDayEndUtc = instant.ToEndOfTzDay(eastern);

Time-zone variants determine the instant's local calendar date and return the current, previous, or next local-day boundary with offset +00:00:

• ToStartOfTzDay() / ToEndOfTzDay()
• ToStartOfPreviousTzDay() / ToEndOfPreviousTzDay()
• ToStartOfNextTzDay() / ToEndOfNextTzDay()

Any input offset is accepted because DateTimeOffset identifies an instant. A midnight inside a time-zone gap advances minute-by-minute to the first valid local minute. An ambiguous midnight selects the earlier UTC instant. End values are one tick before the following valid local-day boundary, so 23-hour and 25-hour days are not treated as fixed 24-hour intervals.

Day-of-week mapping

DayOfWeekType day = value.ToDayOfWeekType();

ToDayOfWeekType() maps the System.DayOfWeek of the value's stored calendar date to Soenneker.Enums.DayOfWeek.DayOfWeekType. It does not perform a time-zone conversion first.