Develop Reference

DateTime get day of year

I want my new year to start at 14 March. Given any DateTime I want to get the day of year? How can I accomplish this with DateTime?
March 14 is the 73rd day of the year (74th in leap years) in the Gregorian calendar. 292 days remain until the end of the year. Is there a way I can define the new year of a year with DateTime?

int DayOfYear(DateTime date, int yearStartMonth, int yearStartDay)
{
var yearStart = new DateTime(d.Year, yearStartMonth, yearStartDay);
if(yearStart > d)
yearStart = yearStart.AddYears(-1);
return (d - yearStart).Days + 1;
}

try to use:
public static int DayOfYear(DateTime date)
{
var startDate= new DateTime(year:date.Year,month:3,day:14); //14 March
var diffDateDays=(date- startDate).Days;
if (diffDateDays > 0) return diffDateDays;
startDate= new DateTime(year:date.Year-1,month:3,day:14); //14 March of previous year
return (date- startDate).Days;
}

Shift date by months but keep the same day

I am trying to shift a date by a number of given months, but also to keep the same day (for example, if the day of the date is Monday, and after shifting with x months the day is Thursday, I want also to subtract 3 days from the new obtained date. This algorithm should add/subtract days depending on the new obtained date, basically providing the closest date that represents the same day of week). As an example, if I have the start date 10.08.2016(Wednesday), and I add 3 months, I will get 10.11.2016(Thursday), so the closest Wednesday to that day is 09.11.2016.
What I managed to make till now looks something like this:
int startDayOfWeek = ((int)startDay.DayOfWeek) == 0 ? 7 : (int)startDay.DayOfWeek;
int newStartDayOfWeek = ((int)startDay.AddMonths(period).DayOfWeek) == 0 ? 7 : (int)startDay.AddMonths(period).DayOfWeek;
int shiftingDays = startDayOfWeek - newStartDayOfWeek;
if (shiftingDays > 3)
shiftingDays -= 7;
where startDay is the start date, and period is the number of months I want to shift to.
But this still fails some times, so any tips would be greately appreciated.
An example when this code fails would be:
startDate = 01.08.2016 (Monday) and period would be 5
After adding 5 months, I get 01.01.2017, which is Sunday, and the closest Monday would be on 02.01.2017, but I get -6 days.

Use this code. The idea is to divide the days by 7, round it, and multiply by 7.
DateTime endDate = startDay.AddMonths((int)period);
endDate = startDay.AddDays((int)Math.Round((double)(endDate - startDay ).Days / 7)*7);

Is that what you are looking for ?
static void Main( string[] args )
{
//DateTime startDay = DateTime.Now;
DateTime startDay = new DateTime( 2016, 8, 1 );
//DateTime startDay = new DateTime( 2016, 8, 10 );
DateTime newDay = startDay.AddMonths( 5 );
int startDayOfWeek = (int)startDay.DayOfWeek;
int newDayOfWeek = (int)newDay.DayOfWeek;
int shift1 = (7 + startDayOfWeek - newDayOfWeek) % 7;
int shift2 = (7 + newDayOfWeek - startDayOfWeek) % 7;
DateTime test = newDay + ((shift1 > shift2) ? - TimeSpan.FromDays( shift2 ) : TimeSpan.FromDays( shift1 ));
}

Calculate 14 days sequence order

Can anyone please help me, how do I calculate fortnightly (14 days) logic using C#?, for a example 14 days start following sequence order on February
Monday start date 8 Feb (next 22 Feb, 7 March, 21 March etc..)
Thursday start date 11 February (next 25 Feb, 10 March, 24 March etc..)
Friday start date 12 February (next 26 Feb, 11 March, 25 March etc..)
My logic is not working for the 14 days day display, because 15 February will come 14 days add, it’ll display “First14days” date 29 February 2016, it is a wrong.
This is C# logic
Day.Days value are Monday, Thursday, Friday etc..
foreach (var Day in day)
{
Example Day.Days = Monday
Int 14days = (((int)Enum.Parse(typeof(DayOfWeek), Day.Days) - (int)today.DayOfWeek + 14) % 7);
DateTime First14days = today.AddDays(14days);
}
My output should be

Simply add TimeSpan.FromDays(14) to any date to get a fortnight further on
DateTime startDate = DateTime.Now;
TimeSpan fortnight = TimeSpan.FromDays(14);
for (int i = 0; i < 6; i++)
{
startDate += fortnight;
Console.WriteLine($"Date for fortnight {i}: {startDate:D}");
}

If I understand correct your question this code will be working for you.
DateTime time = DateTime.Now;
DateTime anotherTime = DateTime.Now;
var allTimes = new HashSet<DateTime>();
for (int i = 0; i < 6; i++)
{
anotherTime = time.AddDays(14);
time = anotherTime;
Console.WriteLine(anotherTime.ToLongDateString());
allTimes.Add(time);
}
// or with your example is possible to like this code.
foreach (var Day in day)
{
anotherTime = Day.AddDays(14);
time = anotherTime;
Console.WriteLine(anotherTime.ToLongDateString());
allTimes.Add(time);
}
First create two DataTime objects. then foreach few times, and in for loop statement set anotherTime = time.AddDays(14) after that set time = anotherTime.
//Output:
//Saturday, February 27, 2016
//Saturday, March 12, 2016
//Saturday, March 26, 2016
//Saturday, April 09, 2016
//Saturday, April 23, 2016
//Saturday, May 07, 2016
EDIT:
I create and HashSet where you can save all you DateTime who you make it.

So here's you all-in-one solution:
// determine the date of next given weekday
DateTime date = GetNextWeekday(DateTime.Today, DayOfWeek.Tuesday);
// create a list and add the start date (if you want)
List<DateTime> fortnights = new List<DateTime>() { date };
// add as many "fortnights" as you like (e.g. 5)
for (int i = 0; i < 5; i++)
{
date = date.Add(TimeSpan.FromDays(14));
fortnights.Add(date);
}
// use your list (here: just for printing the list in a console app)
foreach (DateTime d in fortnights)
{
Console.WriteLine(d.ToLongDateString());
}
Method to get the next weekday, from:
https://stackoverflow.com/a/6346190/2019384
public static DateTime GetNextWeekday(DateTime start, DayOfWeek day)
{
// The (... + 7) % 7 ensures we end up with a value in the range [0, 6]
int daysToAdd = ((int) day - (int) start.DayOfWeek + 7) % 7;
return start.AddDays(daysToAdd);
}

Getting year and week from date

I need to return year and week of a given date. Sounds simple. But to be right 2012-01-01 have to return 2011-52, because week 1 in 2012 starts January 2th.
To find the week, I use:
GregorianCalendar calw = new GregorianCalendar(GregorianCalendarTypes.Localized);
return calw.GetWeekOfYear(DateTime.Parse("2012-01-01"), CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday).ToString();
this return 52. (correct)
But how do I get the Year?
edit:
With the help from here: http://codebetter.com/petervanooijen/2005/09/26/iso-weeknumbers-of-a-date-a-c-implementation/
This seems to work:
private int weekYear(DateTime fromDate)
{
GregorianCalendar cal = new GregorianCalendar(GregorianCalendarTypes.Localized);
int week = weekNumber(fromDate);
int month = cal.GetMonth(fromDate);
int year = cal.GetYear(fromDate);
//week starts after 31st december
if (week > 50 && month == 1)
year = year - 1;
//week starts before 1st January
if (week < 5 && month == 12)
year = year + 1;
return year;
}
private int weekNumber(DateTime fromDate)
{
// Get jan 1st of the year
DateTime startOfYear = fromDate.AddDays(-fromDate.Day + 1).AddMonths(-fromDate.Month + 1);
// Get dec 31st of the year
DateTime endOfYear = startOfYear.AddYears(1).AddDays(-1);
// ISO 8601 weeks start with Monday
// The first week of a year includes the first Thursday
// DayOfWeek returns 0 for sunday up to 6 for saterday
int[] iso8601Correction = { 6, 7, 8, 9, 10, 4, 5 };
int nds = fromDate.Subtract(startOfYear).Days + iso8601Correction[(int)startOfYear.DayOfWeek];
int wk = nds / 7;
switch (wk)
{
case 0:
// Return weeknumber of dec 31st of the previous year
return weekNumber(startOfYear.AddDays(-1));
case 53:
// If dec 31st falls before thursday it is week 01 of next year
if (endOfYear.DayOfWeek < DayOfWeek.Thursday)
return 1;
else
return wk;
default: return wk;
}
}

Noda Time handles this for you very easily:
Noda Time v1.x
using System;
using NodaTime;
public class Test
{
static void Main()
{
LocalDate date = new LocalDate(2012, 1, 1);
Console.WriteLine($"WeekYear: {date.WeekYear}"); // 2011
Console.WriteLine($"WeekOfWeekYear: {date.WeekOfWeekYear}"); // 52
}
}
Noda Time v2.x
using System;
using NodaTime;
using NodaTime.Calendars;
public class Test
{
static void Main()
{
LocalDate date = new LocalDate(2012, 1, 1);
IWeekYearRule rule = WeekYearRules.Iso;
Console.WriteLine($"WeekYear: {rule.GetWeekYear(date)}"); // 2011
Console.WriteLine($"WeekOfWeekYear: {rule.GetWeekOfWeekYear(date)}"); // 52
}
}
That's using the ISO calendar system where the week year starts in the first week with at least 4 days in that year. (Like CalendarWeekRule.FirstFourDayWeek.) If you want a different calendar system, specify it in the LocalDate constructor. Week year rules are handled slightly differently between 1.x and 2.x.
EDIT: Note that this gives the right value for both this situation (where the week-year is less than the calendar year) and the situation at the other end of the year, where the week-year can be more than the calendar year. For example, December 31st 2012 is in week 1 of week-year 2013.
That's the beauty of having a library do this for you: its job is to understand this sort of thing. Your code shouldn't have to worry about it. You should just be able to ask for what you want.

You can get the weeknumber according to the CalendarWeekRule in this way:
var d = new DateTime(2012, 01, 01);
System.Globalization.CultureInfo cul = System.Globalization.CultureInfo.CurrentCulture;
var firstDayWeek = cul.Calendar.GetWeekOfYear(
d,
System.Globalization.CalendarWeekRule.FirstDay,
DayOfWeek.Monday);
int weekNum = cul.Calendar.GetWeekOfYear(
d,
System.Globalization.CalendarWeekRule.FirstFourDayWeek,
DayOfWeek.Monday);
int year = weekNum >= 52 && d.Month == 1 ? d.Year - 1 : d.Year;
You probably want to compare CalendarWeekRule.FirstDay with CalendarWeekRule.FirstFourDayWeek. On this way you get the weeknumber and the year (DateTime.Year-1 if they differ).
CultureInfo.Calendar Property
Calendar.GetWeekOfYear Method
CalendarWeekRule Enumeration

That is just an edge case which you will have to add special code for. Get the year from the date string and then if the week = 52 and the month = 1 then subtract one from the year.

I have solving similar problem where the result should be in "YYYYWW" format. I wanted avoid hardcoded dates and using 3rd party libraries.
My test case was date 1.1.2017 which should return week 201652 (Iso YearWeek)
To get week number I have used thread: Get the correct week number of a given date which returns week number without the year.
Finally the correct year I got from Monday(first day of iso week) of required date:
// returns only week number
// from [Get the correct week number of a given date] thread
public static int GetIso8601WeekOfYear(DateTime time)
{
// Seriously cheat. If its Monday, Tuesday or Wednesday, then it'll
// be the same week# as whatever Thursday, Friday or Saturday are,
// and we always get those right
DayOfWeek day = CultureInfo.InvariantCulture.Calendar.GetDayOfWeek(time);
if (day >= DayOfWeek.Monday && day <= DayOfWeek.Wednesday)
{
time = time.AddDays(3);
}
// Return the week of our adjusted day
var week = CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(time, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
return week;
}
// returns int YearWeek in format "YYYYWW"
public static int GetIso8601YearWeekOfYear(DateTime time)
{
var delta = (-((time.DayOfWeek - CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek + 7) % 7));
var firstDayofWeek = time.AddDays(delta); // takeMonday
var week = GetIso8601WeekOfYear(time);
var yearWeek = (firstDayofWeek.Year * 100) + week;
return yearWeek;
}

In my approach I'm taking advantage of the fact, that GetWeekOfYear() displays a correct ISO-8601 week number for days with the same year as Thursday of the same week. So I look for Thursday that belongs to the same week as a given date, and then call GetWeekOfYear() on it.
I can't do that trick to get a correct year, as there's no iso8601-compliant method for this, so I make a year adjustment if Thursday belongs to a different year than a given date.
The solution is basically a three-liner:
using System.Globalization;
namespace TESTS
{
class Program
{
static void Main(string[] args)
{
//sample dates with correct week numbers in comments:
string[] dats = new string[] {
"2011-12-31","2012-01-01" //1152
,"2012-12-31","2013-01-01" //1301
,"2013-12-31","2014-01-01" //1401
,"2014-12-31","2015-01-01" //1501
,"2015-12-31", "2016-01-01" //1553
};
foreach (string str in dats)
{
Console.WriteLine("{0} {1}", str, GetCalendarWeek(DateTime.Parse(str)));
}
Console.ReadKey();
}
public static int GetCalendarWeek(DateTime dat)
{
CultureInfo cult = System.Globalization.CultureInfo.CurrentCulture;
// thursday of the same week as dat.
// value__ for Sunday is 0, so I need (true, not division remainder %) mod function to have values 0..6 for monday..sunday
// If you don't like casting Days to int, use some other method of getting that thursday
DateTime thursday = dat.AddDays(mod((int)DayOfWeek.Thursday-1,7) - mod((int)dat.DayOfWeek-1,7));
//week number for thursday:
int wk = cult.Calendar.GetWeekOfYear(thursday, cult.DateTimeFormat.CalendarWeekRule, cult.DateTimeFormat.FirstDayOfWeek);
// year adjustment - if thursday is in different year than dat, there'll be -1 or +1:
int yr = dat.AddYears(thursday.Year-dat.Year).Year;
// return in yyww format:
return 100 * (yr%100) + wk;
}
// true mod - helper function (-1%7=-1, I need -1 mod 7 = 6):
public static int mod(int x, int m)
{
return (x % m + m) % m;
}
}

How to calculate financial year start and end dates from financial year's month end value?

I have a financial year's month end value 2.
How would i calculate the financial year DateTime startDate and DateTime endDate from that value?

You can do:
DateTime startDate = new DateTime(DateTime.Today.Year, 2, 1); // 1st Feb this year
DateTime endDate = new DateTime(DateTime.Today.Year+1, 2, 1).AddDays(-1); // Last day in January next year
Does that solve your problem?

I assume you mean Feb by 2.
This code should do this:
DateTime start = new DateTime(2010,2,1);
DateTime end = start.AddMonths(12).AddDays(-1);
Console.WriteLine(start);
Console.WriteLine(end);
Output:
01-Feb-10 12:00:00 AM
31-Jan-11 12:00:00 AM

Here is my version for calculating the Fiscal Year Start Date. It checks the StartMonth against the current month, and will adjust the year.
private DateTime? FiscalYearStartDate() {
int fyStartMonth = 2;
var dte = new DateTime(DateTime.Today.Year, fyStartMonth, 1); // 1st April this year
if (DateTime.Today.Month >= fyStartMonth) {
//Do nothing, since this is the correct calendar year for this Fiscal Year
} else {
//The FY start last calendar year, so subtract a year
dte = dte.AddYears(-1);
}
return dte;
}
You can easily calculate the End Date like others have done, by adding +1 Year, and then subtracting 1 Day (thanks to Johannes Rudolph).
DateTime endDate = new DateTime(DateTime.Today.Year+1, 2, 1).AddDays(-1);

If your current date is 14/01/2021
Then the Indian financial Year is 01/04/2020 to 31/03/2021
Use the following code for perfect output.
DateTime CurrentDate = DateTime.Now;
int CurrentMonth = CurrentDate.Month;
if (CurrentMonth >= 4)//4 is the first month of the financial year.
{
txtFromDate.Text = new DateTime(CurrentDate.Year, 4, 1).ToString(CS.ddMMyyyy);
txtToDate.Text = new DateTime(CurrentDate.Year + 1, 4, 1).AddDays(-1).ToString(CS.ddMMyyyy);
}
else
{
txtFromDate.Text = new DateTime(CurrentDate.Year - 1, 4, 1).ToString(CS.ddMMyyyy);
txtToDate.Text = new DateTime(CurrentDate.Year, 4, 1).AddDays(-1).ToString(CS.ddMMyyyy);
}

public static (DateTime, DateTime) GetCurrentFinacialYearDateRange()
{
if(DateTime.Now.Month >= 7)
{
DateTime startDate = new DateTime(DateTime.Today.Year, 7, 1); // 1st July this year
DateTime endDate = new DateTime(DateTime.Today.Year + 1, 7, 1).AddDays(-1); // Last day in June next year
return (startDate, endDate);
}
else
{
DateTime startDate = new DateTime(DateTime.Today.Year-1, 7, 1); // 1st July this year
DateTime endDate = new DateTime(DateTime.Today.Year, 7, 1).AddDays(-1); // Last day in June next year
return (startDate, endDate);
}
}