AJ Bell says that the price range for the IPO has been set at £1.54 to £1.66 per ordinary share.
This implies a market capitalisation of between £626 million and £675 million when dealing begins.
AJ Bell follows rival platform Transact, whose parent Integrafin floated earlier this year with an estimated initial market value of a similar £650m. Fellow platform Nucleus is also considering a float.
Customers and other investors will be able to apply for shares in AJ Bell from today.
Andy Bell, chief executive of AJ Bell, said today: “There has been significant interest in our IPO which reflects the potential for expansion in our market, the strength of our business model and our track record of sustainable growth.
“The application period for the IPO is due to open later today and our customers will be able to apply for shares via our investment platform where they will find the prospectus to help inform their decision.”
Shares will be sold by certain existing shareholders, directors and employees.
There will be a targeted offering to institutional investors and shares will also be offered to AJ Bell customers. The prospectus is out today.
Final pricing is expected to be announced on or around 7 December, with conditional dealings expected to begin on the London Stock Exchange at 8 am on the same day. Unconditional dealing is expected to commence on or around 12 December.
Numis Securities is handling the float.
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