Jonathan Traub was supposed to spend his family vacation in Breckenridge, Colo., skiing and roasting marshmallows.
Instead, Mr. Traub, the head of Deloitte’s tax-policy practice in Washington, has been holed up in the resort town, producing tax-analysis documents and recording podcasts for clients, trying to explain sweeping tax changes in real time.
On Monday afternoon, he explained the newest provisions of the bill in a webcast with colleagues. Then he hit the slopes.
“I snuck out with my wife to do some runs on the mountain,” Mr. Traub said. “After an hour and a half, I came back to 35 emails in my inbox.”
The sweeping tax legislation that raced through Congress could be signed by President Trump by the end of the year — just as the accounting industry would normally be shifting into holiday mode.
That will not be happening this year. The writing, rewriting and re-rewriting of the tax code has sent tax professionals into a frantic hyperdrive.
Late nights spent scrutinizing the new rules in the office have fueled UberEats and other food delivery services. Christmas shopping? Forget about it. Long-scheduled holiday trips are being delayed or interrupted.
PricewaterhouseCoopers, one of the Big Four accounting firms, is not rescinding its tradition of shutting down the entire firm from Christmas to New Year’s Day.
But that’s basically a technicality.
“People and teams are going to have to figure out what they need to do to make sure we’re serving our clients appropriately during a difficult time,” said Len Combs, the firm’s chief United States auditor.
Because the tax overhaul — the first of its scope in more than three decades — is coming so late in the year, it is setting off a mad dash by public companies. They are required to report the effects of the new law in their financial statements to shareholders in the same quarter that the law becomes enacted, even if the measures themselves go into effect later.
Finishing the necessary analysis on time will be tough. Companies whose fiscal year closes on Dec. 31 or Jan. 31, as is the case for many retailers, will have just a few weeks to produce quarterly and annual financial statements for investors that reflect the new tax system.
“Maybe 50 percent of our clients were following the debate and knew it was headed this way, but I’ve been surprised by the numbers of clients who, by their own admissions, didn’t think this would happen,” said Kate Barton, the vice chairwoman of tax services for the Americas at Ernst & Young. “Maybe 30 to 40 percent of the heads of tax at corporate clients are scrambling to model out the new law and its impact on their businesses.”
A recent Ernst & Young webcast about tax changes for wealthy clients drew 4,671 people. One this week for corporate clients drew more than 12,000 participants, Ms. Barton said.
All this is a headache — possibly a migraine — for many companies and individuals.
For many tax professionals, it’s thrilling.
“This has, in some ways, been my Super Bowl,” said Dustin Stamper, a Washington-based director at Grant Thornton, an audit, tax and advisory firm. “It’s been the most exciting time of my career.”
As various tax proposals emerged throughout the fall, transmogrifying as they moved through the legislative process, Mr. Stamper and his team gathered in conference rooms, scribbling on whiteboards, trying to pin down moving targets.
At the moment, many companies are most concerned with ensuring that their year-end financial statements are accurate. They are hoping the Securities and Exchange Commission will allow some extra time to make calculations and tweak documents.
But large multinational companies, particularly technology and pharmaceutical firms, are also fixated on provisions — such as a one-time tax on offshore profits — that could cause their business strategies and legal structures to fundamentally change.
Corporations that have manufacturing or other operations overseas, or that have highly indebted businesses that will not be as able to deduct interest payments from their taxes, could spend the first half of 2018 restructuring to adapt to the new tax code.
“The reality is, for certain companies, their tax profile is going to look a lot different,” said Mr. Combs of PricewaterhouseCoopers. “Companies are going to have to think through the implications of where they establish their manufacturing locations. Where do they own their intellectual property rights?”
That is why Scott A. Hodge, president of the Tax Foundation, a conservative-leaning think tank, has not been sleeping much lately.
“There’s an adrenaline that comes with that — that’s part of the fun,” he said. “But I’ve lost track of whatever day it is.”
Last year, Mr. Hodge projected that Americans would spend billions of hours filling out corporate income tax returns. This year, though, corporate tax compliance could be even more time-consuming — and therefore more expensive.
“Companies, especially large, publicly traded ones, will be spending more on tax advice than ever before,” he said. “The transition between one tax regime and another is so complicated that they will have to really reach out beyond their internal capabilities to make sure they get it right.”
That is great news for accounting and tax firms.
Several said more clients have signed up for their services and that inquiries from prospective customers have doubled from last year. Matthew Becker, who leads the national tax office for BDO, said the company had increased hiring and pulled in employees from other divisions to help analyze tax data.
At KPMG, analysts spent last weekend poring over the final proposal unveiled by Congress late Friday. By Monday morning, they had produced a 165-page overview, which they later updated. Building managers in the firm’s Washington office had to double-check that the heat and lights, normally controlled by automatic timers, were left on for employees.
“There was lots of pizza day and night,” said Jeffrey C. LeSage, the Americas vice chairman of KPMG’s tax practice.
Working in Colorado as his son played a video game nearby, Mr. Traub said he was looking forward to a lull.
“Once the dust settles on the vote, I’ll hopefully have a little more time to spend with my family,” he said.