It turns out September, not April, may be federal taxpayers’ worst nightmare.

The end of the government’s fiscal year usually brings an orgy of spending as agencies look at their budgets, see extra cash lying around, and figure they’d better use it all up or risk it getting cut in the future.

The “use it or lose it” mentality explains why the Defense Department spent $9,241 on a Wexford leather chair, $2.3 million on crab and another $2.3 million on lobster tails in September, according to a study released Thursday by OpenTheBooks.

Taxpayers shelled out $97 billion on contracts in September, including a staggering $53 billion in the final week — seven days that cost more than the entire month of August.

“In the final month of the fiscal year, federal agencies scramble to spend what’s left in their annual budget; agencies worry spending less than their budget allows might prompt Congress to appropriate less money in the next fiscal year,” said the report from the government-spending watchdog group. “To avoid this, federal agencies choose to embark on an annual shopping spree rather than admit they can operate on less.”

As might be expected, the Defense Department was the biggest spender, and the most money went to big-ticket necessities such as fixed-wing aircraft.

But there were also the lobster tail and crab, $163,636 spent on paint brushes, and $7.6 million on workout equipment — including ski equipment for “adults and junior” earmarked to Misawa Air Base in Japan.

The lobster tail purchases in September were a bit more than 10 percent of what the federal government spent on the delicacy the entire year, suggesting only a slightly elevated rate of spending.

But more than a third of the $721,661 agencies spent on pianos came in September.

And while taxpayers bought $1.6 million worth of golf carts in fiscal 2018, 42 percent of that was spent in the last four weeks. The same with the government’s bill for china tableware, OpenTheBooks’ founder and CEO Adam Andrzejewski said.

“This year-end spending habit is one of the most deceptive budgetary tactics in use in Washington,” said Curtis Kalin, spokesman for Citizens Against Government Waste. “It’s deeply ingrained in the culture of federal bureaucrats, and it perpetuates the myth we can never stop spending.”

Yet the data shows the final-month binge is getting worse. Last year’s $97 billion marks a 16 percent increase from 2017 and a 39 percent increase from 2015.

“As the national debt surpasses $22 trillion, it’s time to end Washington’s use-it-or-lose-it spending culture,” Mr. Andrzejewski said. “Ending this wasteful phenomenon would go a long way toward generating big savings and winning the public’s trust.”

No aspect of government seemed immune from the urge to binge.

President Trump’s executive office blew through $26.8 million, the report found — up from $24.9 million in 2017.

As the large Defense Department share of spending indicates, much of the contract spending was with companies noted for their expertise in weapons and intelligence technology.

The report showed Lockheed Martin was the largest recipient of cash in the final month, raking in $8.7 billion. It was followed by Boeing with $5.1 billion and Raytheon at $3.3 billion, while Northrop Grumman was paid $1.7 billion.

Many of the smaller purchases might have raised taxpayers’ eyebrows.

For example, federal agencies spent $490.6 million on furniture in the month, including the Defense Department’s $9,341 Wexford chair.

Taxpayers also splurged on one federal agency’s $11,800 tournament-level foosball table, records showed.

Neither the White House’s Office of Management and Budget nor press officers at the Pentagon responded to phone calls and e-mails about the end-of-fiscal-year spending and some specific purchases.

OpenTheBooks’ analysis also showed how the year-end blowout reflects the extent to which Washington and a handful of states have come to absorb so much taxpayer money.

September 2018 was a very good month for the constellation of service agencies and contractors tied to the federal government, as the Washington-Virginia-Maryland corridor was showered with $25 billion, records show.

That haul dwarfed the next largest, geographically, which saw Texas take home $8.9 billion and California $7.14 billion.

While there does not appear to be a quick solution to the long-standing problem, Mr. Kalin noted there is always pending legislation that would reward bonuses to those agencies that prove an ability to cut their budget.

“But the incentives are all backwards now, and this boils down to baseline spending accounting,” he said, citing the federal government’s novel practice of beginning each year with every agency starting at the same amount it received in the previous budget and increasing from there.

“If you had zero-based budgeting that would help a lot, too,” Mr. Kalin said. “But there’s no allegiance in Washington to being thrifty, and so the problem just continues no matter who is president.”