Friday, May 25, 2012

How do I calculate someone"s age in C#?


Given a DateTime representing their birthday, how do I calculate someone's age?



Source: Tips4all
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24 comments:

  1. UserMay 25, 2012 at 6:18 AM

    For some reason Jeff's code didn't seem simple enough. To me this seems simpler and easier to understand:

    DateTime now = DateTime.Today;
    int age = now.Year - bday.Year;
    if (bday > now.AddYears(-age)) age--;

    ReplyDelete
  2. UserMay 25, 2012 at 6:18 AM

    This is a strange way to do it, but if you format the date to yyyymmdd and subtract the date of birth from the current date then drop the last 4 digits you've got the age :)

    I don't know C#, but I believe this will work in any language.

    20080814 - 19800703 = 280111


    Drop the last 4 digits = 28.

    C# Code:

    int now = int.Parse(DateTime.Today.ToString("yyyyMMdd"));
    int dob = int.Parse(dateDOB.ToString("yyyyMMdd"));
    string dif = (now - dob).ToString();
    string age = "0";
    if (dif.Length > 4)
    age = dif.Substring(0, dif.Length - 4);

    ReplyDelete
  3. UserMay 25, 2012 at 6:18 AM

    I don't know how the wrong solution can be accepted.
    The correct C# snippet was written by Michael Stum

    Here is a test snippet:

    DateTime bDay = new DateTime(2000, 2, 29);
    DateTime now = new DateTime(2009, 2, 28);
    MessageBox.Show(string.Format("Test {0} {1} {2}",
    CalculateAgeWrong1(bDay, now),
    CalculateAgeWrong2(bDay, now),
    CalculateAgeCorrect(bDay, now)));


    Here you have the methods:

    public int CalculateAgeWrong1(DateTime birthDate, DateTime now)
    {
    return new DateTime(now.Subtract(birthDate).Ticks).Year - 1;
    }

    public int CalculateAgeWrong2(DateTime birthDate, DateTime now)
    {
    int age = now.Year - birthDate.Year;
    if (now < birthDate.AddYears(age)) age--;
    return age;
    }

    public int CalculateAgeCorrect(DateTime birthDate, DateTime now)
    {
    int age = now.Year - birthDate.Year;
    if (now.Month < birthDate.Month || (now.Month == birthDate.Month && now.Day < birthDate.Day)) age--;
    return age;
    }

    ReplyDelete
  4. UserMay 25, 2012 at 6:18 AM

    I am late to the party, but here's a one-liner:

    int age = new DateTime(DateTime.Now.Subtract(birthday).Ticks).Year-1;

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  5. UserMay 25, 2012 at 6:18 AM

    I don't think any of the answers so far provide for cultures that calculate age differently. See, for example, East Asian Age Reckoning versus that in the West.

    Any real answer has to include localization. The Strategy Pattern would probably be in order in this example.

    ReplyDelete
  6. UserMay 25, 2012 at 6:18 AM

    My suggestion

    int age = (int) ((DateTime.Now - bday).TotalDays/365.255);


    That seems to have the year changing on the right date. (I spot tested up to age 107)

    ReplyDelete
  7. UserMay 25, 2012 at 6:18 AM

    The simple answer to this is to apply AddYears as shown below because this is the only native method to add years to the 29th of Feb. of leap years and obtain the correct result of the 28th of Feb. for common years.

    Some feel that 1th of Mar. is the birthday of leaplings but neither .Net nor any official rule supports this, nor does common logic explain why some born in February should have 75% of their birthdays in another month.

    Further, an Age method lends itself to be added as an extension to DateTime. By this you can obtain the age in the simplest possible way:

    int age = birthDate.Age();

    public static class DateTimeExtensions
    {
    /// <summary>
    /// Calculates the age in years of the current System.DateTime object today.
    /// </summary>
    /// <param name="birthDate">The date of birth</param>
    /// <returns>Age in years today. 0 is returned for a future date of birth.</returns>
    public static int Age(this DateTime birthDate)
    {
    return Age(birthDate, DateTime.Today);
    }
    /// <summary>
    /// Calculates the age in years of the current System.DateTime object on a later date.
    /// </summary>
    /// <param name="birthDate">The date of birth</param>
    /// <param name="laterDate">The date on which to calculate the age.</param>
    /// <returns>Age in years on a later day. 0 is returned as minimum.</returns>
    public static int Age(this DateTime birthDate, DateTime laterDate)
    {
    int age;
    age = laterDate.Year - birthDate.Year;
    if (age > 0)
    {
    age -= Convert.ToInt32(laterDate.Date < birthDate.Date.AddYears(age));
    }
    else
    {
    age = 0;
    }
    return age;
    }
    }


    }

    Now, run this test:

    class Program
    {
    static void Main(string[] args)
    {
    RunTest();
    }

    private static void RunTest()
    {
    DateTime birthDate = new DateTime(2000, 2, 28);
    DateTime laterDate = new DateTime(2011, 2, 27);
    string iso = "yyyy-MM-dd";
    for (int i = 0; i < 3; i++)
    {
    for (int j = 0; j < 3; j++)
    {
    Console.WriteLine("Birth date: " + birthDate.AddDays(i).ToString(iso) + " Later date: " + laterDate.AddDays(j).ToString(iso) + " Age: " + birthDate.AddDays(i).Age(laterDate.AddDays(j)).ToString());
    }
    }
    Console.ReadKey();
    }
    }


    The critical date example is this:

    Birth date: 2000-02-29 Later date: 2011-02-28 Age: 11

    Output:

    {
    Birth date: 2000-02-28 Later date: 2011-02-27 Age: 10
    Birth date: 2000-02-28 Later date: 2011-02-28 Age: 11
    Birth date: 2000-02-28 Later date: 2011-03-01 Age: 11
    Birth date: 2000-02-29 Later date: 2011-02-27 Age: 10
    Birth date: 2000-02-29 Later date: 2011-02-28 Age: 11
    Birth date: 2000-02-29 Later date: 2011-03-01 Age: 11
    Birth date: 2000-03-01 Later date: 2011-02-27 Age: 10
    Birth date: 2000-03-01 Later date: 2011-02-28 Age: 10
    Birth date: 2000-03-01 Later date: 2011-03-01 Age: 11
    }


    And for the later date 2012-02-28:

    {
    Birth date: 2000-02-28 Later date: 2012-02-28 Age: 12
    Birth date: 2000-02-28 Later date: 2012-02-29 Age: 12
    Birth date: 2000-02-28 Later date: 2012-03-01 Age: 12
    Birth date: 2000-02-29 Later date: 2012-02-28 Age: 11
    Birth date: 2000-02-29 Later date: 2012-02-29 Age: 12
    Birth date: 2000-02-29 Later date: 2012-03-01 Age: 12
    Birth date: 2000-03-01 Later date: 2012-02-28 Age: 11
    Birth date: 2000-03-01 Later date: 2012-02-29 Age: 11
    Birth date: 2000-03-01 Later date: 2012-03-01 Age: 12
    }


    /gustav

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  8. UserMay 25, 2012 at 6:18 AM

    This is the version we use here. It works, and it's fairly simple. It's the same idea as Jeff's but I think it's a little clearer because it separates out the logic for subtracting one, so it's a little easier to understand.

    public static int GetAge(this DateTime dateOfBirth, DateTime dateAsAt)
    {
    return dateAsAt.Year - dateOfBirth.Year - (dateOfBirth.DayOfYear < dateAsAt.DayOfYear ? 0 : 1);
    }


    You could expand the ternary operator to make it even clearer, if you think that sort of thing is unclear.

    Obviously this is done as an extension method on DateTime, but clearly you can grab that one line of code that does the work and put it anywhere. Here we have another overload of the Extension method that passes in DateTime.Now, just for completeness.

    ReplyDelete
  9. UserMay 25, 2012 at 6:18 AM

    I've spent some time working on this and came up with this to calculate someone's age in years, months and days. I've tested against the Feb 29th problem and leap years and it seems to work, I'd appreciate any feedback:

    public void LoopAge(DateTime myDOB, DateTime FutureDate)
    {
    int years = 0;
    int months = 0;
    int days = 0;

    DateTime tmpMyDOB = new DateTime(myDOB.Year, myDOB.Month, 1);

    DateTime tmpFutureDate = new DateTime(FutureDate.Year, FutureDate.Month, 1);

    while (tmpMyDOB.AddYears(years).AddMonths(months) < tmpFutureDate)
    {
    months++;
    if (months > 12)
    {
    years++;
    months = months - 12;
    }
    }

    if (FutureDate.Day >= myDOB.Day)
    {
    days = days + FutureDate.Day - myDOB.Day;
    }
    else
    {
    months--;
    if (months < 0)
    {
    years--;
    months = months + 12;
    }
    days +=
    DateTime.DaysInMonth(
    FutureDate.AddMonths(-1).Year, FutureDate.AddMonths(-1).Month
    ) + FutureDate.Day - myDOB.Day;

    }

    //add an extra day if the dob is a leap day
    if (DateTime.IsLeapYear(myDOB.Year) && myDOB.Month == 2 && myDOB.Day == 29)
    {
    //but only if the future date is less than 1st March
    if (FutureDate >= new DateTime(FutureDate.Year, 3, 1))
    days++;
    }

    }

    ReplyDelete
  10. UserMay 25, 2012 at 6:18 AM

    Keeping it simple (and possibly stupid:)).

    DateTime birth = new DateTime(1975, 09, 27, 01, 00, 00, 00);
    TimeSpan ts = DateTime.Now - birth;
    Console.WriteLine("You are approximately " + ts.TotalSeconds.ToString() + " seconds old.");

    ReplyDelete
  11. UserMay 25, 2012 at 6:18 AM

    2 Main problems to solve are:

    1. Calculate Exact age - in years, months, days, etc.

    2. Calculate Generally perceived age - people usually do not care how old they exactly are, they just care when their birthday in the current year is.



    Solution for 1 is obvious:

    DateTime birth = DateTime.Parse("1.1.2000");
    DateTime today = DateTime.Today; //we usually don't care about birth time
    TimeSpan age = today - birth; //.NET FCL should guarantee this as precise
    double ageInDays = age.TotalDays; //total number of days ... also precise
    double daysInYear = 365.2425; //statistical value for 400 years
    double ageInYears = ageInDays / daysInYear; //can be shifted ... not so precise




    Solution for 2 is the one which is not so precise in determing total age, but is perceived as precise by people. People also usually use it, when they calculate their age "manually":

    DateTime birth = DateTime.Parse("1.1.2000");
    DateTime today = DateTime.Today;
    int age = today.Year - birth.Year; //people perceive their age in years
    if (
    today.Month < birth.Month
    ||
    ((today.Month == birth.Month) && (today.Day < birth.Day))
    )
    {
    age--; //birthday in current year not yet reached, we are 1 year younger ;)
    //+ no birthday for 29.2. guys ... sorry, just wrong date for birth
    }


    Notes to 2.:


    This is my preferred solution
    We cannot use DateTime.DayOfYear or TimeSpans, as they shift number of days in leap years
    I have put there little more lines for readability


    Just one more note ... I would create 2 static overloaded methods for it, one for universal usage, second for usage-friendliness:

    public static int GetAge(DateTime bithDay, DateTime today)
    {
    //chosen solution method body
    }

    public static int GetAge(DateTime birthDay)
    {
    return GetAge(birthDay, DateTime.Now);
    }

    ReplyDelete
  12. UserMay 25, 2012 at 6:18 AM

    Many years ago, to provide an age calculator gimmick on my website, I wrote a function to calculate age to a fraction. This is a quick port of that function to C# (from the PHP version). I'm afraid I haven't been able to test the C# version, but hope you enjoy all the same!

    (Admittedly this is a bit gimmicky for the purposes of showing user profiles on Stack Overflow, but maybe readers will find some use for it. :-))

    double AgeDiff(DateTime date1, DateTime date2) { double years = date2.Year - date1.Year; /* * If date2 and date1 + round(date2 - date1) are on different sides * of 29 February, then our partial year is considered to have 366 * days total, otherwise it's 365. Note that 59 is the day number * of 29 Feb. */ double fraction = 365 + (DateTime.IsLeapYear(date2.Year) && date2.DayOfYear >= 59 && (date1.DayOfYear < 59 || date1.DayOfYear > date2.DayOfYear) ? 1 : 0); /* * The only really nontrivial case is if date1 is in a leap year, * and date2 is not. So let's handle the others first. */ if (DateTime.IsLeapYear(date2.Year) == DateTime.IsLeapYear(date1.Year)) return years + (date2.DayOfYear - date1.DayOfYear) / fraction; /* * If date2 is in a leap year, but date1 is not and is March or * beyond, shift up by a day. */ if (DateTime.IsLeapYear(date2.Year)) { return years + (date2.DayOfYear - date1.DayOfYear - (date1.DayOfYear >= 59 ? 1 : 0)) / fraction; } /* * If date1 is not on 29 February, shift down date1 by a day if * March or later. Proceed normally. */ if (date1.DayOfYear != 59) { return years + (date2.DayOfYear - date1.DayOfYear + (date1.DayOfYear > 59 ? 1 : 0)) / fraction; } /* * Okay, here date1 is on 29 February, and date2 is not on a leap * year. What to do now? On 28 Feb in date2's year, the ``age'' * should be just shy of a whole number, and on 1 Mar should be * just over. Perhaps the easiest way is to a point halfway * between those two: 58.5. */ return years + (date2.DayOfYear - 58.5) / fraction;}

    ReplyDelete
  13. UserMay 25, 2012 at 6:18 AM

    Another function, not my me but found on the web and a bit refined:

    public static int GetAge(DateTime birthDate){ DateTime n = DateTime.Now; // To avoid a race condition around midnight int age = DateTime.Now.Year - birthDate.Year; if (n.Month < birthDate.Month || (n.Month == birthDate.Month && n.Day < birthDate.Day)) age--; return age;}

    Just two things that come into my mind: What about people from countries that do not use the gregorian calendar? DateTime.Now is in the server-specific culture i think. I have absolutely 0 knowledge about actually working with Asian calendars and I do not know if there is an easy way to convert dates between calendars, but just in case you're wondering about those chinese guys from the year 4660 :-)

    ReplyDelete
  14. UserMay 25, 2012 at 6:18 AM

    Here is a solution.

    DateTime dateOfBirth = new DateTime(2000, 4, 18);
    DateTime currentDate = DateTime.Now;

    int ageInYears = 0;
    int ageInMonths = 0;
    int ageInDays = 0;

    ageInDays = currentDate.Day - dateOfBirth.Day;
    ageInMonths = currentDate.Month - dateOfBirth.Month;
    ageInYears = currentDate.Year - dateOfBirth.Year;

    if (ageInDays < 0)
    {
    ageInDays += DateTime.DaysInMonth(currentDate.Year, currentDate.Month);
    ageInMonths = ageInMonths--;

    if (ageInMonths < 0)
    {
    ageInMonths += 12;
    ageInYears--;
    }
    }
    if (ageInMonths < 0)
    {
    ageInMonths += 12;
    ageInYears--;
    }

    Console.WriteLine("{0}, {1}, {2}", ageInYears, ageInMonths, ageInDays);

    ReplyDelete
  15. UserMay 25, 2012 at 6:18 AM

    The best way that I know of because of leap years and everything is:

    DateTime birthDate = new DateTime(2000,3,1);int age = (int)Math.Floor((DateTime.Now - birthDate).TotalDays / 365.25D);

    Hope this helps.

    ReplyDelete
  16. UserMay 25, 2012 at 6:18 AM

    This is simple and appears to be accurate for my needs. I am making an assumption for the purposes of leap years that regardless of when the person chooses to celebrate the birthday they are not technically a year older until a full 365 days has passed since there last birthday (i.e 28th February does not make them a year older)

    DateTime now = DateTime.Today;
    DateTime birthday = new DateTime(1991, 02, 03);//3rd feb

    int age = now.Year - birthday.Year;

    if (now.Month < birthday.Month || (now.Month == birthday.Month && now.Day < birthday.Day))//not had bday this year yet
    age--;

    return age;


    Let us know if you spot any problems ;)

    ReplyDelete
  17. UserMay 25, 2012 at 6:18 AM

    I have created a SQL Server User Defined Function to calculate someone's age, given their birthdate. This is useful when you need it as part of a query:

    using System;
    using System.Data;
    using System.Data.Sql;
    using System.Data.SqlClient;
    using System.Data.SqlTypes;
    using Microsoft.SqlServer.Server;

    public partial class UserDefinedFunctions
    {
    [SqlFunction(DataAccess = DataAccessKind.Read)]
    public static SqlInt32 CalculateAge(string strBirthDate)
    {
    DateTime dtBirthDate = new DateTime();
    dtBirthDate = Convert.ToDateTime(strBirthDate);
    DateTime dtToday = DateTime.Now;

    // get the difference in years
    int years = dtToday.Year - dtBirthDate.Year;
    // subtract another year if we're before the
    // birth day in the current year
    if (dtToday.Month < dtBirthDate.Month || (dtToday.Month == dtBirthDate.Month && dtToday.Day < dtBirthDate.Day))
    years--;
    int intCustomerAge = years;
    return intCustomerAge;
    }
    };

    ReplyDelete
  18. UserMay 25, 2012 at 6:18 AM

    Would this work?

    public override bool IsValid(DateTime value)
    {
    _dateOfBirth = value;

    var yearsOld = (double) (DateTime.Now.Subtract(_dateOfBirth).TotalDays/365);

    if (yearsOld > 18)
    return true;
    return false;
    }

    ReplyDelete
  19. UserMay 25, 2012 at 6:18 AM

    I use this:

    public static class DateTimeExtensions
    {
    public static int Age(this DateTime birthDate)
    {
    return Age(birthDate, DateTime.Now);
    }
    public static int Age(this DateTime birthDate, DateTime offsetDate)
    {
    int result;

    result = offsetDate.Year - birthDate.Year;
    if (offsetDate.DayOfYear < birthDate.DayOfYear) result--;

    return result;
    }
    }

    ReplyDelete
  20. UserMay 25, 2012 at 6:18 AM

    private int GetAge(int _year, int _month, int _day
    {
    DateTime yourBirthDate= new DateTime(_year, _month, _day);

    DateTime todaysDateTime = DateTime.Today;
    int noOfYears = todaysDateTime.Year - yourBirthDate.Year;
    if (DateTime.Now.Month < yourBirthDate.Month ||
    (DateTime.Now.Month == yourBirthDate.Month && DateTime.Now.Day < yourBirthDate.Day))
    {
    noOfYears--;
    }
    return noOfYears;
    }

    ReplyDelete
  21. UserMay 25, 2012 at 6:18 AM

    The simplest way I've ever found is this. It works correctly for the US and western europe locales. Can't speak to other locales, especially places like China. 4 extra compares, at most, following the initial computation of age.

    public int AgeInYears( DateTime birthDate , DateTime referenceDate )
    {
    Debug.Assert(
    referenceDate >= birthDate ,
    "birth date must be on or prior to the reference date" ) ;

    DateTime birth = birthDate.Date ;
    DateTime reference = referenceDate.Date ;
    int years = ( reference.Year - birth.Year ) ;

    //
    // an offset of -1 is applied if the birth date has
    // not yet occurred in the current year.
    //
    if ( reference.Month > birth.Month ) ;
    else if ( reference.Month < birth.Month ) --years ;
    else // in birth month
    {
    if ( reference.Day < birth.Day ) --years ;
    }

    return years ;

    }

    ReplyDelete
  22. UserMay 25, 2012 at 6:18 AM

    The following approach (extract from Time Period Library for .NET class DateDiff) considers the calendar of the culture info:

    // ----------------------------------------------------------------------
    private static int YearDiff( DateTime date1, DateTime date2 )
    {
    return YearDiff( date1, date2, DateTimeFormatInfo.CurrentInfo.Calendar );
    } // YearDiff

    // ----------------------------------------------------------------------
    private static int YearDiff( DateTime date1, DateTime date2, Calendar calendar )
    {
    if ( date1.Equals( date2 ) )
    {
    return 0;
    }

    int year1 = calendar.GetYear( date1 );
    int month1 = calendar.GetMonth( date1 );
    int year2 = calendar.GetYear( date2 );
    int month2 = calendar.GetMonth( date2 );

    // find the the day to compare
    int compareDay = date2.Day;
    int compareDaysPerMonth = calendar.GetDaysInMonth( year1, month1 );
    if ( compareDay > compareDaysPerMonth )
    {
    compareDay = compareDaysPerMonth;
    }

    // build the compare date
    DateTime compareDate = new DateTime( year1, month2, compareDay,
    date2.Hour, date2.Minute, date2.Second, date2.Millisecond );
    if ( date2 > date1 )
    {
    if ( compareDate < date1 )
    {
    compareDate = compareDate.AddYears( 1 );
    }
    }
    else
    {
    if ( compareDate > date1 )
    {
    compareDate = compareDate.AddYears( -1 );
    }
    }
    return year2 - calendar.GetYear( compareDate );
    } // YearDiff


    Usage:

    // ----------------------------------------------------------------------
    public void CalculateAgeSamples()
    {
    PrintAge( new DateTime( 2000, 02, 29 ), new DateTime( 2009, 02, 28 ) );
    // > Birthdate=29.02.2000, Age at 28.02.2009 is 8 years
    PrintAge( new DateTime( 2000, 02, 29 ), new DateTime( 2012, 02, 28 ) );
    // > Birthdate=29.02.2000, Age at 28.02.2012 is 11 years
    } // CalculateAgeSamples

    // ----------------------------------------------------------------------
    public void PrintAge( DateTime birthDate, DateTime moment )
    {
    Console.WriteLine( "Birthdate={0:d}, Age at {1:d} is {2} years", birthDate, moment, YearDiff( birthDate, moment ) );
    } // PrintAge

    ReplyDelete
  23. UserMay 25, 2012 at 6:18 AM

    Here's a DateTime extender that adds the age calculation to the DateTime object.

    public static class AgeExtender
    {
    public static int GetAge(this DateTime dt)
    {
    int d = int.Parse(dt.ToString("yyyyMMdd"));
    int t = int.Parse(DateTime.Today.ToString("yyyyMMdd"));
    return (t-d)/10000;
    }
    }

    ReplyDelete
  24. UserMay 25, 2012 at 6:18 AM

    I've made one small change to Mark Soen's answer: I've rewriten the third line so that the expression can be parsed a bit more easily.

    public int AgeInYears(DateTime bday)
    {
    DateTime now = DateTime.Today;
    int age = now.Year - bday.Year;
    if (bday.AddYears(age) > now)
    age--;
    return age;
    }


    I've also made it into a function for the sake of clarity.

    ReplyDelete

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