What?
An article to document how I calculated the start and end dates of when Daylight Savings Time is in effect.

Why?
Admittedly, most of Zoho apps have this built-in but here's some snippets of code in case you need them.

How?
I will use this to amend and refine but here's the snippets for the various DSTs around the world.

US (Except Arizona, Hawaii and US Territories?):
  • DST Start Starts Second Sunday in March at 2:00
  • DST End Ends First Sunday in November at 2:00
//
// Starts Second Sunday in March at 2:00
v_FirstMonthDate = toTime(zoho.currentdate.toString("yyyy") + "-03-08 02:00:00");
//
// Ends First Sunday in November at 2:00
v_LastMonthDate = toTime(zoho.currentdate.toString("yyyy") + "-11-01 02:00:00");
//
// loop through each day in a week to get the start and end dates
for each v_DayIndex in {0,1,2,3,4,5,6}
{
    v_CheckDateStart = v_FirstMonthDate.addDay(v_DayIndex);
    if(v_CheckDateStart.toString("E")=="Sun")
    {
        v_DST_StartTime = v_CheckDateStart;
    }
    v_CheckDateEnd = v_LastMonthDate.addDay(v_DayIndex);
    if(v_CheckDateEnd.toString("E")=="Sun")
    {
        v_DST_EndTime = v_CheckDateEnd;
    }
}	
info "Start Date (Current Year): " + v_DST_StartTime.toString("EEEE, yyyy-MM-dd HH:mm");
info "End Date (Current Year): " + v_DST_EndTime.toString("EEEE, yyyy-MM-dd HH:mm");
//
// Starts Second Sunday in March at 2:00
v_FirstMonthDate = toTime(zoho.currentdate.addYear(1).toString("yyyy") + "-03-08 02:00:00");
//
// Ends First Sunday in November at 2:00
v_LastMonthDate = toTime(zoho.currentdate.addYear(1).toString("yyyy") + "-11-01 02:00:00");
//
// loop through each day in a week to get the start and end dates
for each v_DayIndex in {0,1,2,3,4,5,6}
{
    v_CheckDateStart = v_FirstMonthDate.addDay(v_DayIndex);
    if(v_CheckDateStart.toString("E")=="Sun")
    {
        v_DST_StartTime = v_CheckDateStart;
    }
    v_CheckDateEnd = v_LastMonthDate.addDay(v_DayIndex);
    if(v_CheckDateEnd.toString("E")=="Sun")
    {
        v_DST_EndTime = v_CheckDateEnd;
    }
}	
info "Start Date (Next Year): " + v_DST_StartTime.toString("EEEE, yyyy-MM-dd HH:mm");
info "End Date (Next Year): " + v_DST_EndTime.toString("EEEE, yyyy-MM-dd HH:mm");
Yields: 
Start Date (Current Year): Sunday, 2021-03-14 02:00
End Date (Current Year): Sunday, 2021-11-07 02:00
Start Date (Next Year): Sunday, 2022-03-13 02:00
End Date (Next Year): Sunday, 2022-11-06 02:00

Europe:
  • DST Start Last Sunday in March at 1:00 UTC
  • DST End Last Sunday in October at 1:00 UTC
//
// Starts Last Sunday in March at 1:00 UTC
v_FromMonthDate1 = toTime(zoho.currentdate.toString("yyyy") + "-04-01 01:00:00");
//
// Ends Last Sunday in October at 1:00 UTC
v_ToMonthDate1 = toTime(zoho.currentdate.toString("yyyy") + "-10-31 01:00:00");
//
// loop through each day in a week to get the start and end dates
for each v_DayIndex in {0,1,2,3,4,5,6}
{
    v_CheckDateStart = v_FromMonthDate1.subDay(v_DayIndex);
    if(v_CheckDateStart.toString("E")=="Sun")
    {
        v_DST_StartTime = v_CheckDateStart;
    }
    v_CheckDateEnd = v_ToMonthDate1.subDay(v_DayIndex);
    if(v_CheckDateEnd.toString("E")=="Sun")
    {
        v_DST_EndTime = v_CheckDateEnd;
    }
}	
//
// output
info "Start Date (Current Year): " + v_DST_StartTime.toString("EEEE, yyyy-MM-dd HH:mm");
info "End Date (Current Year): " + v_DST_EndTime.toString("EEEE, yyyy-MM-dd HH:mm");
//
// *********************************************************
//
// Starts Last Sunday in March at 1:00 UTC
v_FromMonthDate1 = toTime(zoho.currentdate.addYear(1).toString("yyyy") + "-04-01 01:00:00");
//
// Ends Last Sunday in October at 1:00 UTC
v_ToMonthDate1 = toTime(zoho.currentdate.addYear(1).toString("yyyy") + "-10-31 01:00:00");
//
// loop through each day in a week to get the start and end dates
for each v_DayIndex in {0,1,2,3,4,5,6}
{
    v_CheckDateStart = v_FromMonthDate1.subDay(v_DayIndex);
    if(v_CheckDateStart.toString("E")=="Sun")
    {
        v_DST_StartTime = v_CheckDateStart;
    }
    v_CheckDateEnd = v_ToMonthDate1.subDay(v_DayIndex);
    if(v_CheckDateEnd.toString("E")=="Sun")
    {
        v_DST_EndTime = v_CheckDateEnd;
    }
}	
info "Start Date (Next Year): " + v_DST_StartTime.toString("EEEE, yyyy-MM-dd HH:mm");
info "End Date (Next Year): " + v_DST_EndTime.toString("EEEE, yyyy-MM-dd HH:mm");
Yields: 
Start Date (Current Year): Sunday, 2021-03-28 01:00
End Date (Current Year): Sunday, 2021-10-31 01:00
Start Date (Next Year): Sunday, 2022-03-27 01:00
End Date (Next Year): Sunday, 2022-10-30 01:00

Additional Note(s):
  • This has not been tested extensively. Do not use if you are unsure it is calculating correctly. I use these to store the values in a table that can be double-checked at a later date.

Source(s):