The Iraq Inquiry should be published in June or July 2016, its author says.
Sir John Chilcot said the two million word report would be finished in April, with two months or so then set aside for national security checks on it.
The mother of a British soldier killed in Iraq said it was "another let-down",
criticising the time taken to publish the inquiry, which began in 2009.
Prime Minister David Cameron said he was "disappointed" and offered resources to speed up the process.
The inquiry is considering how UK forces came to participate in the US-led invasion of Iraq in 2003 and its aftermath.
The new publication timetable was set out in a letter to Mr Cameron on the
inquiry's website.
In his letter, Sir John says the text of his report should be completed in the week starting 18 April 2016, at which point the process of national security checking would begin.
Such checking is "normal and necessary" with inquiries handling large amounts of sensitive material, he said.
It will ensure that national security and Article 2 of the European Convention on Human Rights, which protects the right to life, are not "inadvertently breached" by publication, he said.
"I consider that once national security checking has been completed it should be possible to agree a date for publication in June or July 2016," he added.