"We estimate that there is a deficiency in the assets on hand to support these balances of approximately A$15m to A$25m," Kelly said in the report.
Initial investigations indicated that the deficiency had accumulated over at least the last 24 months.
Factors impacting the final shortfall include unrealised profit or loss positions in relation to open trades, currency fluctuations and ongoing market fluctuations.
The exact size will only be known once all investor positions have been closed out, the report said.
While the Australian Financial Services Licence and the Derivatives Issuer Licence (New Zealand) have been suspended by the Australian Securities and Investment Commission and the Financial Markets Authority, investors are still able to close out their positions during the suspension, the report said.
The administrators have undertaken an initial analysis of the funds flow process on the Halifax's "MT4" and "MT5" platforms.
"The process of allocating and tracing individual investor funds will likely be a complex and lengthy process," the report said.
The administrators said they exected to further update investors in mid to late February.
Over the past six years local investors poured tens of millions of dollars through online broker Halifax New Zealand, before it followed its Australian parent abruptly into administration.
The Australian company also promoted itself using celebrity "ambassador" former Australian test cricket captain Mark Taylor who had previously endorsed the business in promotional videos on the Halifax website and on YouTube.