Like rivals including IG Group and CMC Markets, Plus500 benefited from the pandemic boom in locked-down Britons taking up trading for the first time in 2020.
It made acquisitions and launched a new "Plus500 Invest" share dealing platform in Europe in the half, and plans further rollout of the platform around the continent this year.
But the company reported a sharp fall in first-half sales as trading levels normalised.
Plus500 said it saw revenues for the six months to July of $346.2 million, down nearly 39% from a record $564.2 million in the same period last year. The pace of new customers joining its platform also fell, to 136,980 from a record high of 198,176.
Both measures remain above pre-pandemic levels, however, and the company said its board expects revenues "to be significantly ahead of current compiled analysts' consensus forecasts" for the year.
CEO, David Zruia, said: "Future growth will be delivered through continued organic investments in our business, our technology and targeted bolt-on acquisitions to further expand our CFD offering, launch new trading products, introduce new financial products and deepen engagement with our customers.
"Having increased our expectations for the outlook for the Group, the Board is increasingly confident that Plus500 will continue to deliver further growth and consistent levels of cash generation over the medium to long term."