Calculate relative time in C#

Question

Given a specific DateTime value, how do I display relative time, like:

• 2 hours ago
• 3 days ago
• a month ago

Answer 1

Here's an implementation I added as an extension method to the DateTime class that handles both future and past dates and provides an approximation option that allows you to specify the level of detail you're looking for ("3 hour ago" vs "3 hours, 23 minutes, 12 seconds ago"):

using System.Text;

/// 

/// Compares a supplied date to the current date and generates a friendly English 
/// comparison ("5 days ago", "5 days from now")
/// 
/// The date to convert
/// When off, calculate timespan down to the second.
/// When on, approximate to the largest round unit of time.
/// 
public static string ToRelativeDateString(this DateTime value, bool approximate)
{
    StringBuilder sb = new StringBuilder();

    string suffix = (value > DateTime.Now) ? " from now" : " ago";

    TimeSpan timeSpan = new TimeSpan(Math.Abs(DateTime.Now.Subtract(value).Ticks));

    if (timeSpan.Days > 0)
    {
        sb.AppendFormat("{0} {1}", timeSpan.Days,
          (timeSpan.Days > 1) ? "days" : "day");
        if (approximate) return sb.ToString() + suffix;
    }
    if (timeSpan.Hours > 0)
    {
        sb.AppendFormat("{0}{1} {2}", (sb.Length > 0) ? ", " : string.Empty,
          timeSpan.Hours, (timeSpan.Hours > 1) ? "hours" : "hour");
        if (approximate) return sb.ToString() + suffix;
    }
    if (timeSpan.Minutes > 0)
    {
        sb.AppendFormat("{0}{1} {2}", (sb.Length > 0) ? ", " : string.Empty, 
          timeSpan.Minutes, (timeSpan.Minutes > 1) ? "minutes" : "minute");
        if (approximate) return sb.ToString() + suffix;
    }
    if (timeSpan.Seconds > 0)
    {
        sb.AppendFormat("{0}{1} {2}", (sb.Length > 0) ? ", " : string.Empty, 
          timeSpan.Seconds, (timeSpan.Seconds > 1) ? "seconds" : "second");
        if (approximate) return sb.ToString() + suffix;
    }
    if (sb.Length == 0) return "right now";

    sb.Append(suffix);
    return sb.ToString();
}