Mayor’s budget might look responsible, but he’s hiking spending at a rate well above inflation.

Someday, Mayor de Blasio may truly show the fiscal discipline that he holds out as a guiding principle of his budgeting. Presenting a preliminary spending plan on Thursday, the mayor combined the bright picture of a city with a record number of jobs and the stern image of a manager responsibly planning for tougher times.

In fact, de Blasio stayed on a track that hikes city spending by a rate far higher than inflation — while avoiding the painful work of squeezing money-saving efficiencies out of an $82 billion-ayear governmental behemoth.

At first blush, his starter budget for the year beginning in July appeared remarkably restrained for a mayor who had previously boosted spending by as much as 7% annually. By one happy measure he had gone up by less than 1%; by another he had stayed below 2%.

But when you stripped away accounting maneuvers and funds provided by the state and federal governments, de Blasio is actually looking forward to hike city outlays by 4.5%.

That’s more than double the rate of inflation. And more than double the 2% cap on spending growth Gov. Cuomo has imposed on state government as well as on other localities.

The good fortune of having robust revenues, which will not continue forever, enabled de Blasio to withstand getting hammered by huge new bills.

Whammy one: The already enormous cost of city pensions is jumping by $600 million to $9.3 billion, based on a recalculations of how many years municipal retirees are projected to live.

Lifespans have increased markedly since benefit levels were set, so de Blasio must put more into the bank in order to meet long-term obligations.

Whammy two: The public hospital system is in such dire fiscal straits that de Blasio is doing a bailout with an immediate injection of $327 million.

Down the road, he faces trends that head toward bankruptcy unless City Hall maintains heavy investments or hospital management pulls off a near-miraculous turnaround.

Due to falling revenue, the system has operated hand-to-mouth for much of de Blasio’s term without mayoral action. Its board and president have been scrambling, at times even to meet payroll.

As long ago as last April, this page raised a warning that Obamacare and the flight of insured patients to major health care institutions had placed the system in severe jeopardy.

Together, the pension and hospital hits, totaling $900 million, explain why de Blasio managed only sprinklings of new money — $4 million here and $10 million there for initiatives like a mental health hotline and expanded gunshot detectors.

Clearly, the hits also forced him to stop bolstering reserve funds that serve as a cushion in downturns and help meet future unfunded liabilities.

While the good times roll, reality looms ever closer.