How do I discover the quarter of a given date

The following are the Quarters for a financial year

April to June          - Q1
July to Sep            - Q2
Oct to Dec             - Q3
Jan to March           - Q4

If the month of an input date lies as above I need the output for in terms of Quarter number.

For Example,

If I give an input date (say january 2nd) , I need the output as Q4.

If I give input as (Jun 5), output should give Q1.

Based on input date I need the Quarter number.

If you prefer short and concise solutions without branching and arrays, here is my preferred solution.

Normal Quarter:

public static int GetQuarter(this DateTime date)
{
    return (date.Month + 2)/3;
}

Financial Year Quarter:

public static int GetFinancialQuarter(this DateTime date)
{
    return (date.AddMonths(-3).Month + 2)/3;
}

Integer division will truncate decimals, giving you an integer result. Place methods into a static class and you will have an extension method to be used as follows:

date.GetQuarter()
date.GetFinancialQuarter()

See dotnetfiddle

You can simply write an extension method to DateTime

public static int GetQuarter(this DateTime date)
{
    if (date.Month >= 4 && date.Month <= 6)
        return 1;
    else if (date.Month >= 7 && date.Month <= 9)
        return 2;
    else if (date.Month >= 10 && date.Month <= 12)
        return 3;
    else 
        return 4;
}

and use it as

DateTime dt = DateTime.Now;
dt.GetQuarter();

This is for the "normal year". I think you can adapt the sample:

string.Format("Q{0}", (date.Month + 2)/3);

The most simple and consistent way of achieving this:

Regular

Math.Ceiling(date.Month / 3.0)

Fiscal (just shifted up with a mod by 2+1 quarters)

Math.Ceiling(date.Month / 3.0 + 2) % 4 + 1

01.01.2016 00:00:00 -> Q1 -> FQ4
01.02.2016 00:00:00 -> Q1 -> FQ4
01.03.2016 00:00:00 -> Q1 -> FQ4
01.04.2016 00:00:00 -> Q2 -> FQ1
01.05.2016 00:00:00 -> Q2 -> FQ1
01.06.2016 00:00:00 -> Q2 -> FQ1
01.07.2016 00:00:00 -> Q3 -> FQ2
01.08.2016 00:00:00 -> Q3 -> FQ2
01.09.2016 00:00:00 -> Q3 -> FQ2
01.10.2016 00:00:00 -> Q4 -> FQ3
01.11.2016 00:00:00 -> Q4 -> FQ3
01.12.2016 00:00:00 -> Q4 -> FQ3

Result is a value between 1 and 4. Nearly any environment has a CEIL function, so this should work on any language as well.

public static int GetQuarter(DateTime date)
{
    int[] quarters = new int[] { 4,4,4,1,1,1,2,2,2,3,3,3 };
    return quarters[date.Month-1];
}