EDF is part of a French-Chinese consortium that was awarded the two-reactor project last year despite criticism from green groups and cost warnings from experts.
"The final project costs are now estimated at £19.6 billion at 2015 rates, an increase of £1.5 billion," EDF said in a communique.
It also warned of a possible delay of 15 months in delivering the first reactor, and nine months for the second.
The announcement came after EDF on June 26 said it was carrying out a "full review" of Hinkley Point's costs and schedule.
Named Hinkley Point C, the project, built in the southwestern English county of Somerset, will provide seven percent of Britain's power needs, according to the British government.
Critics have focused on the proposed design, which uses a novel EPR reactor that has run into huge problems of cost overruns and delays at sites in France and Finland.
They also question an electricity price guarantee to EDF of £92.5 for every megawatt hour of power produced by Hinkley over the following 35 years, rising with inflation, despite falling energy prices.
On June 23, Britain's National Audit Office (NAO) lashed the scheme, saying the government had "locked consumers into a risky and expensive project with uncertain strategic and economic benefits."
Environmentalists are fiercely opposed, urging the government to instead focus on renewable sources like wind and solar power to meet Britain's energy needs.
The project, scheduled under the deal to start producing electricity in 2025, has a projected operational lifetime of 60 years.
The deal was approved by Prime Minister Theresa May's government only last September, amid uncertainty about the future of the British economy caused by Brexit.
Heavily-indebted EDF, mainly owned by the French government, is funding around two-thirds of the cost and its Chinese partner the remainder.