But shares rose 3.2% to 362.3p in morning trading the peer-to-peer lender said it expects its performance to improve in 2019.
Funding Circle, which had a tough start to trading with shares falling below its initial public offering price of 440p, said its loss before tax ballooned to £50.7mln last year from £36.3mln in 2017.
The adjusted loss (EBITDA) was £28.5mln in 2018, compared to £251mln the prior year.
The group spent £24.5mln on product development, including the IT platform, while corporate expenses rose to £11.0mln due to the additional costs of operating as a listed company.
Revenues beat guidance
Revenue rose by 55% to £141.9mln, ahead of the 50% growth the company said it expected at the time of the IPO.
Loans under management, excluding property, gained 55% to £3.15bn as originations jumped 40% to £2.29bn.
Funding Circle said net lending to small and medium enterprises in the UK last year was £723mln, higher than the £515mln by all high street banks combined.
US loans under management topped US$1bn, ahead of about 98% of FDIC-insured banks in 2018 that held a combined US$939mln.
Funding Circle positive on 2019 outlook
In 2019, the firm expects revenues above £200mln and the adjusted EBITDA loss to reduce due to central costs falling to 20% of revenue.
The guidance excludes the adoption of IFRS 16 accounting measures and new investor products.
New investor products are expected to add about £2-3mln to both revenue and adjusted earnings (EBITDA) in 2019, and IFRS16 is projected to add a further £5mln to adjusted EBITDA and have a “minimal impact” on the loss before tax.
"As we look ahead to the rest of 2019, we remain focused on continuing our strategy of investing for growth and building on our number one market positions across the UK, US, Germany and the Netherlands,” said chief executive and founder, Samir Desai.
"We have exciting plans to enter the Canadian market later this year and to launch two new institutional investor products in 2019 that will significantly increase the universe of investors who can access Funding Circle loans."