Maryland transit officials planning a 16-mile light-rail Purple Line in the Washington suburbs told Montgomery County Council members Tuesday that they now estimate the project’s total construction costs at $2.45 billion, up $21 million from a July projection.

State officials, who addressed the council during a regular update on the project, didn’t cite a reason for the increase. On such a massive project, $21 million represents an uptick of less than 1 percent. However, it is the latest in a steady climb. The Post reported in mid-September that the July estimate of $2.427 billion was $56 million higher than a January estimate of $2.37 billion.

The project’s true cost won’t be known until the state awards what is expected to be a 35-year contract to a team of private companies that would design, build and help finance the project in exchange for operating and maintaining the line. Those bids are due in January, and state officials have said they expect to choose a private partner by spring 2015.

Jamie Kendrick, deputy executive director of transit development for the Maryland Transit Administration, told the council that keeping such a mega-project on schedule would be key in controlling costs. Every month of delay, he said, is estimated to add about $7 million in inflationary costs.

State officials have said they hope to begin construction on the light-rail line between Bethesda and New Carrollton, in Prince George’s County, in 2015 and begin train service in 2020.