Having floated at 160p per share, giving a market capitalisation of £651 million, the shares have rallied to 295p, with the market cap now standing at nearly £1.2 billion.
Index provider FTSE Russell named AJ Bell as one of the likely additions to the FTSE 250 ahead of the reshuffle, which will be based on today's closing prices and announced after the market close tomorrow. The index changes will come into effect on 15 March.
A host of top UK small cap fund managers have snapped up the shares, according to Refintiv data.
They include Citywire AAA-rated Nick Williamson, manager of the Merian UK Smaller Companies Focus fund, Harry Nimmo, Citywire AA-rated manager of Standard Life Investments UK Smaller Companies, and fellow AA-rated managers Anthony Cross and Julian Fosh, who run the Liontrust Special Situations and Liontrust UK Smaller Companies funds.
AJ Bell customers were also able to get in at the 160p flotation price, after the online stockbroker reserved a slice of the IPO for retail investors.
The shares' rise has catapulted his stake into the fourth largest position in his £3.4 billion Invesco Income fund, representing 3.3% of the portfolio. That was despite Invesco selling 42% of its stake in the business as part of the flotation. The fund group remains AJ Bell's largest shareholder, holding just over a quarter of the shares.
Phoenix is the frontrunner for promotion, with a £5 billion market cap, boosted by its acquisition of Standard Life Aberdeen's (SLA) insurance business last year.
Just Eat comeback
Another contender, although not named by FTSE Russell in its detailing of indicative changes based on Friday's closing prices, is Just Eat (JE).
The online delivery firm's 4.1% rise since the start of the week has taken its market cap to £4.89 billion, just above Aveva's £4.88 billion. Shares in Aveva have dipped 1% since the start of the week.
Just Eat's promotion would mark a swift return to the blue-chip index after relegation in December last year.
After peaking at 890p in February last year, shares in Just Eat endured a heavy fall to 551p by December.
'The shares’ slide began when then chief executive Peter Plumb announced a plan to invest £50 million in delivery services, subsequently stepped up to £55 million to £60 million,' said Russ Mould, investment director at AJ Bell.
'That move was designed to improve customer service and combat other online platform rivals but investors took fright amid (unsubstantiated) talk that Uber Eats was looking to acquire Deliveroo, which itself raised its game with the launch of its Marketplace+ platform.'
While 2019 has brought more uncertainty with the departure of chief executive Peter Plumb, January's announcement that 2018 forecasts would be surpassed, and higher sales expectations for 2019, have helped drive the shares to 734p.
Wood Group faces drop
Wood Group (WG) is the prime contender for FTSE 100 relegation, with shares in the oil services company having fallen 29% since its promotion to blue-chip status at the end of September last year.
That coincided with a fall in the oil price, from around $85 a barrel in early October to $65 today.
'Wood Group’s latest stay in the FTSE seems destined to be as brief as its previous ones,' said Mould.
'Promotions in April 2008, March 2011 and September 2012 were swiftly followed by demotion in September 2008, September 2011 and September 2013.'
Also at risk of relegation is gambling group GVC (GVC), with shares having tumbled 41% from August's high.
Contenders for promotion from the FTSE Small Cap index to the FTSE 250 include Kier (KIE), the Neil Woodford-backed construction company whose market cap has swelled to £827 million after a rights issue.
Pets at Home (PETSP) could also get the nod, after the 25% rally in shares of the pet supplies retailer since the turn of the year.
Analysts at Numis highlighted the potential investment trusts movers in the reshuffle.
'We expect Edinburgh Dragon (EFM) to be relegated from the FTSE 250 to the FTSE Small Cap, after its tender offer,' they said.
‘We note that Law Debenture (LWDB) is close to promotion to the FTSE 250, and behind it a number of other investment companies – including NextEnergy Solar (NESF) and Schroder Oriental Income (SOI) – are next in the rankings for promotion to the FTSE 250.'