Gibbons said it was unsure whether high-value sales completed by September 30 would be enough to enable it to achieve first half budgets, particularly due to weak Asian trading.
But the group said it believed it would hit market full-year forecasts due to initiatives in place, benefits from acquisitions and sales of rare high quality collectibles.
It said more of its auctions this year were due to take place in the second six months of the financial year rather than the first.
"The group is therefore budgeted to deliver materially higher revenues and profits in the second half," it said.
Total online revenues were up 22% compared to the year to March 31, 2014. "We have continued to achieve double-digit growth in our Total online revenues in the current financial year to date," it said.
It added that its new Marketplace product was yet to materially add to the online revenue increase, but said: "We are beginning to see signs of sentiment improving, and expect this to translate into improved traffic and conversion in the coming months."
Cost savings implemented in the first half, excluding exceptional costs, are expected to lead to annual savings of £1.4mln.
Shares rose 0.5p to 154.5p in early London trading.