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Package date provides functionality for working with dates.

This package introduces a light-weight Date type that is storage-efficient and convenient for calendrical calculations and date parsing and formatting (including years outside the [0,9999] interval).

It also provides

  • clock.Clock which expresses a wall-clock style hours-minutes-seconds with millisecond precision.
  • timespan.DateRange which expresses a period between two dates.
  • timespan.TimeSpan which expresses a duration of time between two instants (see RFC5545).
  • view.VDate which wraps Date for use in templates etc.

See package documentation for full documentation and examples.

See also period.Period, which implements periods corresponding to the ISO-8601 form (e.g. "PT30S").


go get


This library has been in reliable production use for some time. Versioning follows the well-known semantic version pattern.

Version 2

Changes since v1:

  • The period.Period type has moved.
  • clock.Clock now has nanosecond resolution (formerly millisecond resolution).
  • date.Date is now an integer that holds the number of days since year zero. Previously, it was a struct based on year 1970.
  • date.Date time conversion methods have more explicit names - see table below.
  • date.Date arithmetic and comparison operations now rely on Go operators; the corresponding methods have been deleted - see table below.
  • date.Date zero value is now year 0 (Gregorian proleptic astronomical) so 1970 will no longer cause issues.
  • date.PeriodOfDays has been moved to timespan.PeriodOfDays
  • date.DateString has been deleted; the SQL driver.Valuer implementation is now pluggable and serves the same purpose more simply.

Renamed methods:

Was Use instead
date.Date.Local date.Date.Midnight
date.Date.UTC date.Date.MidnightUTC
date.Date.In date.Date.MidnightIn

Deleted methods and functions:

Was Use instead
date.Date.Add +
date.Date.Sub -
date.Date.IsZero == 0
date.Date.Equal ==
date.Date.Before <
date.Date.After >
date.IsLeap gregorian.IsLeap
date.DaysIn gregorian.DaysIn
timespan.DateRange.Normalise (not needed)

Any v1 dates persistently stored as integers will be incorrect; these can be corrected by adding 719162 (date.ZeroOffset) to them, which is the number of days between year zero (v2) and 1970 (v1). Dates stored as strings will be unaffected.


This package follows very closely the design of package time in the standard library; many of the Date methods are implemented using the corresponding methods of the time.Time type and much of the documentation is copied directly from that package.

The original Good Work on which this was based was done by Filippo Tampieri at Fxtlabs.