How would you calculate the age in C# using date of birth (considering leap years)

Question

Here is a problem. I have seen many solutions, but no one seems to be fulfilling the criteria I want...

I want to display the age in this format

20 y         


        

Answer 1

Age is pretty tricky. Here's the relevant excerpts from a struct I use.

public struct Age
{
    private readonly Int32 _years;
    private readonly Int32 _months;
    private readonly Int32 _days;
    private readonly Int32 _totalDays;

    /// 

    /// Initializes a new instance of .
    /// 
    /// The date and time when the age started.
    /// The date and time when the age ended.
    /// This 
    public Age(DateTime start, DateTime end)
        : this(start, end, CultureInfo.CurrentCulture.Calendar)
    {
    }

    /// 

    /// Initializes a new instance of .
    /// 
    /// The date and time when the age started.
    /// The date and time when the age ended.
    /// Calendar used to calculate age.
    public Age(DateTime start, DateTime end, Calendar calendar)
    {
        if (start > end) throw new ArgumentException("The starting date cannot be later than the end date.");

        var startDate = start.Date;
        var endDate = end.Date;

        _years = _months = _days = 0;
        _days += calendar.GetDayOfMonth(endDate) - calendar.GetDayOfMonth(startDate);
        if (_days < 0)
        {
            _days += calendar.GetDaysInMonth(calendar.GetYear(startDate), calendar.GetMonth(startDate));
            _months--;
        }
        _months += calendar.GetMonth(endDate) - calendar.GetMonth(startDate);
        if (_months < 0)
        {
            _months += calendar.GetMonthsInYear(calendar.GetYear(startDate));
            _years--;
        }
        _years += calendar.GetYear(endDate) - calendar.GetYear(startDate);

        var ts = endDate.Subtract(startDate);
        _totalDays = (Int32)ts.TotalDays;
    }

    /// 

    /// Gets the number of whole years something has aged.
    /// 
    public Int32 Years
    {
        get { return _years; }
    }

    /// 

    /// Gets the number of whole months something has aged past the value of .
    /// 
    public Int32 Months
    {
        get { return _months; }
    }

    /// 

    /// Gets the age as an expression of whole months.
    /// 
    public Int32 TotalMonths
    {
        get { return _years * 12 + _months; }
    }

    /// 

    /// Gets the number of whole weeks something has aged past the value of  and .
    /// 
    public Int32 Days
    {
        get { return _days; }
    }

    /// 

    /// Gets the total number of days that have elapsed since the start and end dates.
    /// 
    public Int32 TotalDays
    {
        get { return _totalDays; }
    }

    /// 

    /// Gets the number of whole weeks something has aged past the value of  and .
    /// 
    public Int32 Weeks
    {
        get { return (Int32) Math.Floor((Decimal) _days/7); }
    }

    /// 

    /// Gets the age as an expression of whole weeks.
    /// 
    public Int32 TotalWeeks
    {
        get { return (Int32) Math.Floor((Decimal) _totalDays/7); }
    }
}

Here's an example unit test that passes:

    [Test]
    public void Should_be_exactly_20_years_old()
    {
        var now = DateTime.Now;
        var age = new Age(now.AddYears(-20), now);

        Assert.That(age, Has.Property("Years").EqualTo(20)
            .And.Property("Months").EqualTo(0)
            .And.Property("Days").EqualTo(0));
    }