A C# UK bank holiday calculator

May 21, 2014

In the UK we’re fortunate enough to get 5 free holidays a year, under the guise of “Bank Holidays”. These are mostly on Mondays and come in January, March/April, May, August and December.

Below is a calculator for working out the dates of these holidays, along with tests for the next 5 years. The class tells you if you’re on a bank holiday, but could be easily changed to return the bank holiday dates. For now, it doesn’t tell you if you’re on the Boxing Day bank holiday.

	public class BankHolidayCalculator
	{
	public bool IsJanuaryBankHolidayMonday(DateTime currentDateTime)
	{
	// January bank holiday falls on the first working day after New Year's day,
	// which is usually January 1st itself.
	DateTime newYearsDay = new DateTime(currentDateTime.Year, 01, 01);
	DateTime bankHoliday = newYearsDay;
	while (IsWorkingDay(bankHoliday.DayOfWeek) == false)
	{
	bankHoliday = bankHoliday.AddDays(1);
	}

	return currentDateTime.Date == bankHoliday.Date;
	}

	public bool IsEasterBankHolidayMonday(DateTime currentDateTime)
	{
	// Easter bank holiday is always the Monday after Easter Sunday.
	DateTime easterSunday = GetEasterSunday(currentDateTime.Year);
	return easterSunday.AddDays(1).Date == currentDateTime.Date;
	}

	public DateTime GetEasterSunday(int year)
	{
	// From http://stackoverflow.com/a/2510411/21574
	int day = 0;
	int month = 0;

	int g = year % 19;
	int c = year / 100;
	int h = (c - (int)(c / 4) - (int)((8 * c + 13) / 25) + 19 * g + 15) % 30;
	int i = h - (int)(h / 28) * (1 - (int)(h / 28) * (int)(29 / (h + 1)) * (int)((21 - g) / 11));

	day = i - ((year + (int)(year / 4) + i + 2 - c + (int)(c / 4)) % 7) + 28;
	month = 3;

	if (day > 31)
	{
	month++;
	day -= 31;
	}

	return new DateTime(year, month, day);
	}

	public bool IsMayBankHolidayMonday(DateTime currentDateTime)
	{
	// The first Monday of May is a bank holiday (May day)
	DateTime firstMayBankHoliday = new DateTime(currentDateTime.Year, 05, 01);
	while (firstMayBankHoliday.DayOfWeek != DayOfWeek.Monday)
	{
	firstMayBankHoliday = firstMayBankHoliday.AddDays(1);
	}

	if (currentDateTime.Date == firstMayBankHoliday.Date)
	return true;

	// The last Monday of May is a bank holiday (Spring bank holiday)
	DateTime lastMayBankHoliday = new DateTime(currentDateTime.Year, 05, 31);
	while (lastMayBankHoliday.DayOfWeek != DayOfWeek.Monday)
	{
	lastMayBankHoliday = lastMayBankHoliday.AddDays(-1);
	}

	if (currentDateTime.Date == lastMayBankHoliday.Date)
	return true;

	return false;
	}

	public bool IsAugustBankHolidayMonday(DateTime currentDateTime)
	{
	// The last Monday of August is a bank holiday
	DateTime augustBankHoliday = new DateTime(currentDateTime.Year, 08, 31);
	while (augustBankHoliday.DayOfWeek != DayOfWeek.Monday)
	{
	augustBankHoliday = augustBankHoliday.AddDays(-1);
	}

	if (currentDateTime.Date == augustBankHoliday.Date)
	return true;
	else
	return false;
	}

	public bool IsDecemberBankHoliday(DateTime currentDateTime)
	{
	// December's bank holiday is the first working day on, or after Boxing day.
	DateTime boxingDay = new DateTime(currentDateTime.Year, 12, 26);
	DateTime bankHoliday = boxingDay;

	if (boxingDay.DayOfWeek == DayOfWeek.Monday)
	bankHoliday = boxingDay.AddDays(1);

	while (IsWorkingDay(bankHoliday.DayOfWeek) == false)
	{
	bankHoliday = bankHoliday.AddDays(1);
	}

	if (currentDateTime.Date == bankHoliday.Date)
	return true;
	else
	return false;
	}

	public bool IsWorkingDay(DayOfWeek dayOfWeek)
	{
	if (dayOfWeek == DayOfWeek.Saturday \|\| dayOfWeek == DayOfWeek.Sunday)
	return false;

	return true;
	}
	}

view raw UKBankHolidayCalculator.cs hosted with ❤ by GitHub

	using System;
	using NUnit.Framework;

	[TestFixture]
	public class BankHolidayCalculatorTests
	{
	[Test]
	[TestCase("Jan 1 2015")]
	[TestCase("Jan 1 2016")]
	[TestCase("Jan 2 2017")]
	[TestCase("Jan 1 2018")]
	[TestCase("Jan 1 2019")]
	[TestCase("Jan 1 2020")]
	public void should_be_january_bank_holiday(string date)
	{
	// Arrange
	DateTime dateTime = DateTime.Parse(date);
	BankHolidayCalculator calculator = new BankHolidayCalculator();

	// Act
	bool isBankHoliday = calculator.IsJanuaryBankHolidayMonday(dateTime);

	// Assert
	Assert.That(isBankHoliday, Is.True);
	}

	[Test]
	public void should_not_be_january_bank_holiday()
	{
	// Arrange
	DateTime dateTime = DateTime.Parse("Jan 1 2017");
	BankHolidayCalculator calculator = new BankHolidayCalculator();

	// Act
	bool isBankHoliday = calculator.IsMayBankHolidayMonday(dateTime);

	// Assert
	Assert.That(isBankHoliday, Is.False);
	}

	[Test]
	[TestCase("May 4 2015")]
	[TestCase("May 25 2015")]
	[TestCase("May 2 2016")]
	[TestCase("May 30 2016")]
	[TestCase("May 1 2017")]
	[TestCase("May 29 2017")]
	public void should_be_may_bank_holiday(string date)
	{
	// Arrange
	DateTime dateTime = DateTime.Parse(date);
	BankHolidayCalculator calculator = new BankHolidayCalculator();

	// Act
	bool isBankHoliday = calculator.IsMayBankHolidayMonday(dateTime);

	// Assert
	Assert.That(isBankHoliday, Is.True);
	}

	[Test]
	public void should_not_be_may_bank_holiday()
	{
	// Arrange
	DateTime dateTime = DateTime.Parse("May 9 2017");
	BankHolidayCalculator calculator = new BankHolidayCalculator();

	// Act
	bool isBankHoliday = calculator.IsMayBankHolidayMonday(dateTime);

	// Assert
	Assert.That(isBankHoliday, Is.False);
	}

	[Test]
	[TestCase("August 31 2015")]
	[TestCase("August 29 2016")]
	[TestCase("August 28 2017")]
	[TestCase("August 27 2018")]
	public void should_be_august_bank_holiday(string date)
	{
	// Arrange
	DateTime dateTime = DateTime.Parse(date);
	BankHolidayCalculator calculator = new BankHolidayCalculator();

	// Act
	bool isBankHoliday = calculator.IsAugustBankHolidayMonday(dateTime);

	// Assert
	Assert.That(isBankHoliday, Is.True);
	}

	[Test]
	public void should_not_be_august_bank_holiday()
	{
	// Arrange
	DateTime dateTime = DateTime.Parse("August 14 2017");
	BankHolidayCalculator calculator = new BankHolidayCalculator();

	// Act
	bool isBankHoliday = calculator.IsMayBankHolidayMonday(dateTime);

	// Assert
	Assert.That(isBankHoliday, Is.False);
	}

	[Test]
	[TestCase("6 April 2015")]
	[TestCase("28 March 2016")]
	[TestCase("17 April 2017")]
	[TestCase("2 April 2018")]
	[TestCase("22 April 2019")]
	[TestCase("13 April 2020")]
	public void should_be_easter_bank_holiday(string date)
	{
	// Arrange
	DateTime dateTime = DateTime.Parse(date);
	BankHolidayCalculator calculator = new BankHolidayCalculator();

	// Act
	bool isBankHoliday = calculator.IsEasterBankHolidayMonday(dateTime);

	// Assert
	Assert.That(isBankHoliday, Is.True);
	}

	[Test]
	public void should_not_be_easter_bank_holiday()
	{
	// Arrange
	DateTime dateTime = DateTime.Parse("April 13 2015");
	BankHolidayCalculator calculator = new BankHolidayCalculator();

	// Act
	bool isBankHoliday = calculator.IsMayBankHolidayMonday(dateTime);

	// Assert
	Assert.That(isBankHoliday, Is.False);
	}

	[Test]
	[TestCase("26 December 2014")]
	[TestCase("28 December 2015")]
	[TestCase("27 December 2016")]
	[TestCase("26 December 2017")]
	[TestCase("26 December 2018")]
	[TestCase("26 December 2019")]
	[TestCase("26 December 2019")]
	[TestCase("28 December 2020")]
	public void should_be_december_bank_holiday(string date)
	{
	// Arrange
	DateTime dateTime = DateTime.Parse(date);
	BankHolidayCalculator calculator = new BankHolidayCalculator();

	// Act
	bool isBankHoliday = calculator.IsDecemberBankHoliday(dateTime);

	// Assert
	Assert.That(isBankHoliday, Is.True);
	}

	[Test]
	public void should_not_be_december_bank_holiday()
	{
	// Arrange
	DateTime dateTime = DateTime.Parse("29 December 2014");
	BankHolidayCalculator calculator = new BankHolidayCalculator();

	// Act
	bool isBankHoliday = calculator.IsMayBankHolidayMonday(dateTime);

	// Assert
	Assert.That(isBankHoliday, Is.False);
	}
	}

view raw UKBankHolidayCalculatorTests.cs hosted with ❤ by GitHub

csharp

I'm Chris Small, a software engineer working in London. This is my tech blog. Find out more about me via Github, Stackoverflow, Resume