|Date of birth||27 June 1984|
|Place of birth||Heidelberg, West Germany|
|Height||1.80 m (5 ft 11 in)|
|2002–2008||1899 Hoffenheim II||112||(77)|
|2009–2016||1899 Hoffenheim II||143||(59)|
|2012||→ Philadelphia Union (loan)||4||(0)|
|* Senior club appearances and goals counted for the domestic league only and correct as of 25 June 2015.
Herdling began his career with SG Heidelberg-Kirchheim and moved later to SpVgg Neckarsteinach in the youth ranks. At the beginning of the 2002–03 season, he joined TSG 1899 Hoffenheim in the Regionalliga Süd. He left Hoffenheim in the 2008–09 season to join SV Waldhof Mannheim.
His first second division match was on 28 March 2008 in the match against FC Augsburg. His first goal in the second division was on 13 April 2008 when he scored the only goal in the loss against Alemannia Aachen.
Kai Herdling played in the first half of the season 2008–09 for the Regionalliga team SV Waldhof Mannheim, but returned to Hoffenheim on 26 January 2009.
On 16 April 2012, Herdling was loaned out to the Philadelphia Union of Major League Soccer, and played for two months. In his time in America, he played in four league matches (starting three) and two Lamar Hunt U.S. Open Cup ties.
In May 2016 he ended his career without having made a single appearance in the 2015-16 season due to a chronic knee injury.
|Club performance||League||Cup||League Cup||Continental||Total|
|2008–09||Waldhof Mannheim||Regionalliga Süd||14||11||0||0||0||0||0||0||14||11|
|2010–11||1899 Hoffenheim II||Regionalliga Süd||30||19||0||0||0||0||0||0||30||19|
|USA||League||Open Cup||League Cup||North America||Total|
|2012||Philadelphia Union||Major League Soccer||4||0||2||0||0||0||0||0||6||0|
Updated 5 June 2012
- "TSG holt Herdling" (in German). kicker.de. 26 January 2010. Retrieved 28 August 2010.
- "Leverkusen blamiert sich in der Provinz" (in German). spiegel.de. 2 December 2003. Retrieved 28 August 2010.
- "Der ewige Herdling" (in German). Rhein-Neckar-Zeitung. 10 August 2013. Retrieved 19 August 2013.
- "Union sign German MF/FW Kai Herdling". Philadelphia Union. 16 April 2012. Retrieved 1 July 2012.
- "Kai Herdling: “I am staying faithful to TSG”". TSG 1899 Hoffenheim. 12 May 2016. Retrieved 23 August 2016.