A UK Vat Calculator written in an OO style

OOVatCalculator.cs

using System;

class Program {
	static void Main() {
		WriteAmount(new DateTime(2008, 11, 01), 1.00M);
		WriteAmount(new DateTime(2009, 01, 01), 1.00M);
		WriteAmount(new DateTime(2010, 12, 01), 1.00M);
		WriteAmount(new DateTime(2011, 12, 01), 1.00M);
	}

	static void WriteAmount(DateTime date, decimal exVatAmount) {
		VatCalculator calculator = VatCalculator.Create(date);

		Console.WriteLine(string.Format("On {0:D}, for an amount of {1:c} the VAT inclusive figure is {2:c} for a rate of {3:p}", date, exVatAmount, calculator.CalculateAmount(exVatAmount), calculator.VatRate));
	}
}

abstract class VatCalculator {
	private static readonly VatCalculator _vatCalculator2008 = new VatCalculator2008();
	private static readonly VatCalculator _vatCalculator2009 = new VatCalculator2009();
	private static readonly VatCalculator _vatCalculator2010 = new VatCalculator2010();
	private static readonly VatCalculator _vatCalculator2011 = new VatCalculator2011();

	public static VatCalculator Create(DateTime date) {
		if(date < new DateTime(2008, 12, 1)) {
			return _vatCalculator2008;
		} else if(date < new DateTime(2010, 1, 1)) {		
			return _vatCalculator2009;
		} else if(date > new DateTime(2011, 1, 4)) {
			return _vatCalculator2011;
		} else {
			return _vatCalculator2010;
		}		
	}

	public abstract decimal VatRate {get; }
	public abstract decimal CalculateAmount(decimal exVatAmount);

	private class VatCalculator2008 : VatCalculator {
		public override decimal VatRate {get {return 0.175M;}}
		public override decimal CalculateAmount(decimal exVatAmount) { return exVatAmount * 1.175M; }
	}
	private class VatCalculator2009 : VatCalculator {
		public override decimal VatRate {get {return 0.15M;}}
		public override decimal CalculateAmount(decimal exVatAmount) { return exVatAmount * 1.15M; }
	}
	private class VatCalculator2010 : VatCalculator {
		public override decimal VatRate {get {return 0.175M;}}
		public override decimal CalculateAmount(decimal exVatAmount) { return exVatAmount * 1.175M; }
	}
	private class VatCalculator2011 : VatCalculator {
		public override decimal VatRate {get {return 0.2M;}}
		public override decimal CalculateAmount(decimal exVatAmount) { return exVatAmount * 1.2M; }
	}
}