Calculating the begin and end of Daylight Saving Time

Friday 16 August 2019 @ 11:32 pm

I am not a big fan of Daylight Saving Time (DST). I even hear some states and countries are talking about dropping it (yeah!). But in the meantime there are plenty of reports that need to adjust the time twice a year. This usually happens when the datetime values are stored in Greenwich Mean Time (GMT) and have to be converted to a local time. Then you need to know when DST begins and ends.

The first two formulas below calculate the beginning and ending dates of DST, based on the year of your transaction date. The third formula uses the first two formulas to make the one-hour adjustment. Substitute your GMT date fields into the first and third formula.

```//DST Start DateVar Start:= Date (Year ({@YourDateTimeGMT}) , 3, 15); DateVar BOM:= Start - Day(Start)+7; DateVar BOW:= BOM - DayOfWeek(BOM) + 8; DateAdd('h', 2, BOW);```

```//DST End {@DST Start} + 238 ;```

```//Adjusted DateTime if {@YourDateTimeGMT} in {@DST Start} to {@DST End} then DateAdd('h', 5, {@YourDateTimeGMT}) else DateAdd('h', 4, {@YourDateTimeGMT})```

(For examples of my most popular formulas, please visit the FORMULAS page on my website.)