[1] Before making his debut for Dundee United, McCallum had three separate spells out on loan, firstly he moved to Forfar Athletic for three months, on 31 December 2011.
[4] After spending many seasons on loan in the lower divisions or as an unused substitute, McCallum finally made his Dundee United debut on 6 May 2014, in a 3–1 Scottish Premiership defeat to Aberdeen.
[8] McCallum left Dundee United in January 2016 by mutual consent, with the player looking to further his career by seeking first-team football.
[10] In August 2016, McCallum signed for Plymouth Argyle as third choice goalkeeper, going on to make just two appearances in the 2016–17 season, both of which were as a substitute in EFL Trophy games, both times taking the place of Vincent Dorel.
[11] McCallum rejected a new contract from Plymouth in the summer of 2017 and signed for Scottish League One club Forfar Athletic.