The cost of repairing the Brooklyn Bridge is expected to hit $811 million — a roughly $200 million increase from estimates made only last year, The Post has learned.

When the mammoth project to renovate the 133-year-old span began in 2010, the price tag was even lower — $508 million.

The nearly 60 percent spike in costs over the years has most recently been attributed to “scope changes” and “unforeseen field conditions,” according to information posted online by the Mayor’s Office of Operations.

The completion date for the new work has been pushed back a year, to April 2017 — four years later than originally announced.

“Big public projects take too long to complete and routinely run over budget,” said Maria Doulis, an analyst for the watchdog Citizens Budget Commission.

“The city has made attempts to be more transparent about this by posting information online, but it’s unclear what actions are being taken to evaluate and address the root causes.”

Doulis adds that the city needs Albany to grant the Transportation Department “design-build authority,” which she claims would save money and accelerate construction work.

With numerous bridge-repair projects ongoing, the CBC estimates the city could save as much as $2 billion over 10 years if it had the same authority the state has for managing bridge construction.

City taxpayers are on the hook for 54 percent of the bridge work – with the feds pitching in on the remaining costs, according to Department of Transportation officials.

They said the newly added work included steel repairs, painting of additional areas and even fixing damage to protective shielding caused by a barge incident.