Cálculo timeago

+(NSString *)getTimeAgo:(NSDate *)fecha
{
    NSString *timeAgo;
    float since_mins,since_hours, since_days, since_months, since_years;

    NSTimeInterval since = fabs([fecha timeIntervalSinceNow]);
    since_mins = (since / 60);
    since_hours = (since_mins / 60);
    since_days = (since_hours / 24);
    since_months = (since_days / 31);
    since_years = (since_months / 365);

    if(since_years >= 1) timeAgo = [NSString stringWithFormat:@"%.f %@",floor(since_years), floor(since_years)==1?@" year ago":@" years ago"];
    else if(since_months >= 1) timeAgo = [NSString stringWithFormat:@"%.f %@",floor(since_months), floor(since_months)==1?@" month ago":@" months ago"];
    else if(since_days >= 1) timeAgo = [NSString stringWithFormat:@"%.f %@",floor(since_days), floor(since_days)==1?@" day ago":@" days ago"];
    else if(since_hours >= 1) timeAgo = [NSString stringWithFormat:@"%.f %@",floor(since_hours), floor(since_hours)==1?@" hour ago":@" hours ago"];
    else if(since_mins >= 1) timeAgo = [NSString stringWithFormat:@"%.f %@",floor(since_mins), floor(since_mins)==1?@" minute ago":@" minutes ago"];
    else if(since == 60) timeAgo = @"1 minute ago";
    else timeAgo = [NSString stringWithFormat:@"%.f %@", since, floor(since_mins)==1?@" second ago":@" seconds ago"];
    return timeAgo;
}