Shares in Asos have fallen sharply despite the online fashion retailer posting a 10% rise in half-year profits to £29.9m.
The firm said retail sales jumped 27% to £1.13bn for the six months to 28 February compared with the same period in the previous year.
The shares fell as Asos said it would spend up to £250m on its operations.
Shares fell more than 7% in morning trading to £64.88, but are still £10 higher than a year ago.
Nicholas Hyett at Hargreaves Lansdown said Asos’s costs “seem to have a life of their own”.
“Any retailer growing at 20%-plus a year will need to invest, but what’s disappointing about Asos is its tendency to underestimate capital expenditure requirements by some tens of millions a year,” he said.
“That the rapid growth isn’t delivering any meaningful margin benefits only adds to the frustration.”
Asos has spent about £95m on its business so far this year.
Half that sum has gone on technology and transformation programmes, with the remainder on infrastructure across its supply chain and head office.
Asos chief executive Nick Beighton said the results showed strong trading amid substantial investment for its future.
“Our customer engagement is going from strength to strength and we’ve achieved more than a billion site visits for the first time,” he said.
The company was aiming for £4bn of net sales to make Asos the “world’s number one destination for fashion-loving 20-somethings”.