# Summer time formulas (aka DST)

**URL:** <https://community.fibery.io/t/summer-time-formulas-aka-dst/9623>\
**Category:** Misc\
**Created:** [September 19, 2025, 12:36pm UTC](https://community.fibery.io/t/summer-time-formulas-aka-dst/9623 "2025-09-19T12:36:18Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![Chr1sG](https://sea2.discourse-cdn.com/flex020/user_avatar/community.fibery.io/chr1sg/32/3941_2.png) [@Chr1sG](https://community.fibery.io/u/Chr1sG)\
**Post date:** [September 19, 2025, 12:36pm UTC](https://community.fibery.io/t/summer-time-formulas-aka-dst/9623/1 "2025-09-19T12:36:18Z")

</div>

Posting here in case it’s useful, and for my own future reference 😉

Simple-ish formulas to check if summer time is in force:

Europe (CEST):

```auto
DateTimeField >=
  Date(Year(DateTimeField), 4, 1) -
    Days(IsoWeekday(Date(Year(DateTimeField), 4, 1))) +
    Hours(1) and
  DateTimeField <
    Date(Year(DateTimeField), 11, 1) -
      Days(IsoWeekday(Date(Year(DateTimeField), 11, 1))) +
      Hours(1)

```

US:

```auto
DateTimeField >=
  Date(Year(DateTimeField), 3, 1) +
    Days(14 - IsoWeekday(Date(Year(DateTimeField), 3, 1))) +
    Hours(Delta + 2) and
  DateTimeField <
    Date(Year(DateTimeField), 11, 1) +
      Days(7 - IsoWeekday(Date(Year(DateTimeField), 11, 1))) +
      Hours(Delta + 2)

```

where `Delta` is time difference in winter from UTC (e.g. 5 for Eastern US)

Australia:

```auto
DateTimeField >=
  Date(Year(DateTimeField), 10, 8) -
    Days(IsoWeekday(Date(Year(DateTimeField), 10, 8))) -
    Hours(8) or
  DateTimeField <
    Date(Year(DateTimeField), 4, 8) -
      Days(IsoWeekday(Date(Year(DateTimeField), 4, 8))) -
      Hours(8)

```

or

```auto
DateTimeField >=
  Date(Year(DateTimeField), 10, 8) -
    Days(IsoWeekday(Date(Year(DateTimeField), 10, 8))) -
    Hours(7) -
    Minutes(30) or
  DateTimeField <
    Date(Year(DateTimeField), 4, 8) -
      Days(IsoWeekday(Date(Year(DateTimeField), 4, 8))) -
      Hours(7) -
      Minutes(30)

```

depending on whether you’re in New South Wales, ACT, Victoria and Tasmania, or in South Australia (or the the New South Wales town of Broken Hill(!) )