Costs for the beleaguered Muskrat Falls hydro development in Labrador are up by another $1 billion.

Nalcor Energy CEO Stan Marshall says the new price tag is $12.7 billion with financing.

That's up from the estimate last year of $11.7 billion and is about $5 billion higher than when the project was sanctioned five years ago.

Marshall took over as head of Nalcor last year and agreed its Muskrat Falls megaproject was a "boondoggle" he would try to fix.

Marshall blames the increases on contractor disputes, higher operating costs, a leaky cofferdam, and delays including a worksite occupation last fall by demonstrators concerned about methylmercury.

Marshall says 75 per cent of construction is now done, up from 48 per cent last May.

First power is expected in 2019 at an estimated cost of 23.3 cents per kilowatt hour before tax.

That's up 8.2 cents from when Muskrat Falls was approved and is more than double recent rates paid by consumers.

Marshall and Premier Dwight Ball have said they'll look at ways to lower those rates to ease average monthly bills that could otherwise go up more than $150 per month.