It may be possible to build the calculation in the script. Or iIf you just need the actual dates, you can download them from a site on the web. Google "Easter dates" and find a suitable source.
While this thread is old, the main question remains. I implemented the algorithm described in http://www.oremus.org/liturgy/etc/ktf/app/easter.html below. If your goal is to compute net working days, you could add indicators for weekends and public holidays in a Master Calendar, and compute the sum of these days between the dates of interest.
// Compute Easter Sunday. Apparently, QLik Sense does not provide this info.
//
// Useful links
// https://www.oremus.org/liturgy/etc/ktf/app/easter.html
// https://almanac.oremus.org/easter/computus/
// https://help.qlik.com/en-US/qlikview/April2020/Subsystems/Client/Content/QV_QlikView/Scripting/dollar-sign-expansion-using-parameters.htm
// We refer to the year number as y (or $1), and use it to calculate the
// g: Golden number
Set GoldenNumber = '(Mod($1, 19) + 1)';
// s: solar correction
// l: lunar correction
Set SolarCorrection= 'Floor(($1-1600)/100) - Floor(($1-1600)/400)';
Set LunarCorrection = 'Floor(((Floor(($1-1400)/100))*8)/25)';
// p': Next we calculate the date of the Paschal full moon, that is, the full moon which Easter is the Sunday after. This is done in several stages.
Set Paschal_uncorr = 'Mod(3 - 11*$(GoldenNumber($1)) + $(SolarCorrection($1)) - $(LunarCorrection($1)), 30)';
// p: Paschal full moon (as the number of days after 21st March)
// apply a minor correction to get the exact date of the Paschal full moon (as the number of days after 21st March)
Set Paschal = 'If($(Paschal_uncorr($1)) = 29 or ($(Paschal_uncorr($1)) = 28 and $(GoldenNumber($1)) > 11), $(Paschal_uncorr($1))-1, $(Paschal_uncorr($1)))';
// d: calculate the 'Dominical number'
// Note that this is the number from which the Dominical letter is determined
Set DominicalNumber = 'Mod($1 + Floor($1/4) - Floor($1/100) + Floor($1/400),7)';
// d': which is the date on which the first Sunday of the year falls
Set FirstSunday = 'Mod(8-$(DominicalNumber($1)), 7)';
// p'': the first date in the year which falls on the same day of the week as the Paschal full moon.
Set FirstDay = 'Mod(31 + 28 + 21 + $(Paschal($1)), 7)';
// x = difference between d' (the first Sunday in the year) and p'' (the day of the week when the Paschal full moon falls)
// with minor correction so that x falls within the range 1-7 instead of 0-6
Set SundayDiff = '(Mod($(FirstSunday($1)) - $(FirstDay($1)) - 1, 7) + 1)';
// number of days Easter falls after 21st March:
Set EasterOffset = '$(Paschal($1)) + $(SundayDiff($1))';
Set Easter = 'Date(MakeDate($1, 3, 21) + $(EasterOffset($1)))';
Let y = Year(Today());
Let g = $(GoldenNumber(Year(Today())));
Let s = $(SolarCorrection(Year(Today())));
Let l = $(LunarCorrection(Year(Today())));
Let p_prime = $(Paschal_uncorr(Year(Today())));
Let p = $(Paschal(Year(Today())));
Let d = $(DominicalNumber(Year(Today())));
Let d_prime = $(FirstSunday(Year(Today())));
Let p_dblprime = $(FirstDay(Year(Today())));
Let x = $(SundayDiff(Year(Today())));
Let e = $(EasterOffset(Year(Today())));
Let Easter_2024 = $(Easter(Year(Today())-1));
Let Easter_ThisYear = $(Easter(Year(Today())));
Let Easter_2026 = $(Easter(2026));
Let Easter_2027 = $(Easter(2027));
Let Easter_2028 = $(Easter(2028));
Let Easter_2029 = $(Easter(2029));
trace >>> Year = $(y);
trace >>> GoldenNumber($(y)) = $(g);
trace >>> SolarCorrection($(y)) = $(s);
trace >>> LunarCorrection($(y)) = $(l);
trace >>> Paschal_uncorr($(y)) = $(p_prime);
trace >>> Paschal($(y)) = $(p);
trace >>> DominicalNumber($(y)) = $(d);
trace >>> FirstSunday($(y)) = $(d_prime);
trace >>> FirstDay($(y)) = $(p_dblprime);
trace >>> SundayDiff($(y)) = $(x);
trace >>> EasterOffset($(y)) = $(e);
trace >>> Easter(2024) = $(Easter_2024);
trace >>> Easter($(y)) = $(Easter_ThisYear);
trace >>> Easter(2026) = $(Easter_2026);
trace >>> Easter(2027) = $(Easter_2027);
trace >>> Easter(2028) = $(Easter_2028);
trace >>> Easter(2029) = $(Easter_2029);
Let y = NULL();
Let g = NULL();
Let s = NULL();
Let l = NULL();
Let p_prime = NULL();
Let p = NULL();
Let d = NULL();
Let d_prime = NULL();
Let p_dblprime = NULL();
Let x = NULL();
Let e = NULL();
Let Easter_2024 = NULL();
Let Easter_ThisYear = NULL();
Let Easter_2026 = NULL();
Let Easter_2027= NULL();
Let Easter_2028 = NULL();
Let Easter_2029 = NULL();
