FM (2009), International Master (2011). Andersen is Denmark's top junior (U20) and in that country's top 10 (September 2014).
Andersen acquired his first IM norm when he scored 6/9 at the Danish Championship in April 2009. His second IM norm came in May 2010 when he against scored 6/9, this time at the Liechtenstein Open. His third IM norm came when with another 6/9, this time at the London Chess Classic Open in December 2010.
Andersen has been competing in rated tournaments since he was 10 or 11, starting with the European U12 Championship in 2006 and in the 2006/2007 Rilton Cup where he scored a creditable 4/9. He built up his early experience in open competition on the Scandinavian circuit and has consistently fought above his weight to improve his chess.
Plunging into the deep end, Andersen played in the International Open in Calvi in 2008 (scoring 2.5/8). Notwithstanding objectively modest results, Andersen's strategy of playing in strong tournaments saw a rapid increase in his playing strength throughout 2008 and most of 2009. He started playing in the Danish Team Championships; competed in the Gausdal Classic GM-B tournament, scoring 3/9, all of which were against titled players; 5.5/10 in the Vesterhavs Tournament; 5.5/10 in the Politiken Cup; and 4/7 in the International Open in Oslo before winning his first tournament when he scored =1st at the 5th Amateur Open in Calvia. He continued his good form scoring 5/9 at the International Open in Ciutat de Palma and 5/7 at the Øbro New Year tournament in Copenhagen. In 2009 he contested the Danish Championship and the Reykjavik Open scoring 6/9 and 5/9 respectively, and amassing ELO points aplenty.
Between April 2008 and July 2009, Andersen had added 316 ELO to take his rating from the nadir of 2020 through to 2336, picking up an FM title along the way.
Andersen continued contesting difficult tournaments, including the 2009/10 Rilton Cup scoring a solid 4.5/9 against 9 opponents including 5 GMs and an IM, and then scored 5.5/9 in the GM tournament in Bronshoj, Denmark. He scored 3.5/10 in a strong Danish Championship 2010, which was good enough to pick up another 12 ELO. There followed 4.6/8 in the Copenhagen Chess Challenge, 6/9 in the 2010 Liechtenstein Open and in June 2010, he defeated his first GM opponent, Heikki Westerinen, at the Sveins 3. Memorial Tournament in Oslo. Andersen has started 2011 with a 6/10 (+5 -2 =3) result in the Tradewise Gibraltar (2011). He scored well (5.5/6) in the Danish Teams Tournament which finished in March, and came 4th in the Landsholdsklassen in April. Relatively meagre pickings followed for some months, scoring 5/9 at the Copenhagen Chess Challenge (although he defeated GM Throstur Thorhallsson), 2.5/9 at the 1st GM international in Cracow and 6/10 in the 2011 Politiken Cup. In October 2011, he came =5th at the 29th Balaton International Festival Open with 6/9 and finished 2011 with a solid 4.5/9 at the 23rd International Chess Festival in Cracow in Poland.
2012 was a very good year for Andersen, starting with some excellent results in team events (see below) and scoring 6.5/9 in the Copenhagen Chess Challenge in May and 6/9 in the Bronshoj GM in June, also in Copenhagen. These added a further 27 points to his rating but both results were just shy of further GM norms. Nevertheless, he won the BSF Cup 2012 in Denmark in October 2012 to win his first GM norm. 2013 started with a solid 6.5/10 at the Reykjavik Open (2013) and continued with a solid 7/10 at the Politiken Cup (2013) and 5.5/9 at the Oslo GM Tournament in September. In 2014, he won the Visma Chess Tournament in Växjö, Sweden ahead of Tiger Hillarp Persson, but didn't acquire his final GM norm.
Andersen first competed in a regional championship during 17th European Youth Championship 2007 (U12) that was held in Sibenik, Croatia, scoring 4.5/9. In the 2008 European Youth Chess Championship (U14), he scored 5/9. In 2009, he again contested the European U14 championship, this time scoring 6.5/9, and placing =6th.
He competed in the 2007 World Youth Championship (U12), scoring 6.5/11 and placing =29th. Persisting with the U14 championship contests that he'd engaged in twice in Europe, Andersen competed in the 2009 World U14 championship, scoring 8/11 and placing =5th. He placed =4th in the 2010 World U16 Youth Championship and even contested the World Junior Championship (2010) in which he scored 7/13 still aged 15. In 2011, he contested the World U16 Championship held in Caldas Novas, scoring 5.5/9. In 2013, he contested the World U18 World Championship, scoring a reasonably creditable 7.5/11 without however troubling the leader board.
Andersen had an excellent rating period leading up to May 2012 in team competition. Playing for Solingen in the 2011-12 Bundesliga, he scored 5.5/8 to help his team to 3rd place in the League. Playing for the team Skanderborg in the Danish Division Tournament of 2011-12, Andersen scored an outstanding 7.5/8 with a TPR of 2758 while in the 2012-13 Division Tournament, he scored 6.5/9, defeating all 3 GMs he played, and scoring another GM norm from the latter result as the former had insufficient GMs to meet the criteria for a GM norm. He scored his 3rd GM norm playing top board for the Danish team Nordea Skanderborg in the European Club Cup (2013). He played reserve for Denmark in the European Team Championship (2013), played for SG Solingen in the 2013 Bundesliga and played board 5 for Denmark in the Chess Olympiad (2014).
In May 2010, Andersen played and lost a two game match against Peter Heine Nielsen by 0-2.