President Trump’s latest tariffs are about to become an unavoidable and expensive reality for American businesses and for people who rely on foreign goods.

Shoppers buying clothes from retailers in China may soon pay more than twice as much, now that a special exemption for lower-value imports is disappearing. And companies involved in international trade must now make even more complicated calculations to decide how much they owe in tariffs.

“Maybe 3 percent of the people are well prepared,” said Jeremy Page, a founding partner of Page Fura, an international trade law firm, whose clients include large companies. “And that might even be charitable.”

Imports from China have been hit with tariffs of 145 percent. That means for every $100 worth of goods a business buys from that country, it has to pay $145 to the federal government. Goods from most other countries have a new 10 percent tax, though that could rise if the countries do not reach trade agreements with the United States by July. And there are separate tariffs on cars, steel and aluminum. Mr. Trump has also said he wants to impose new tariffs on pharmaceuticals and computer chips.

Mr. Trump contends that the tariffs will encourage businesses to produce goods in the United States. The tariffs on Chinese goods will almost certainly reduce imports from the country. But American businesses will not be able to quickly get goods from elsewhere — U.S. imports from China totaled $439 billion last year — and they will end up owing huge amounts in tariffs.

Who pays the tariffs?

Mr. Trump has said tariffs are a tax on other countries, but, overwhelmingly, American businesses importing the goods pay the tariffs to the Customs and Border Protection when goods enter the United States. Importers may pass some or all of the cost of the tariff to consumers through higher prices.

“In the short term, prices are definitely going to increase,” said Daniel J. Barabino, chief operating officer at Top Banana, a fruit distributor based at the Hunts Point Produce Market in the Bronx, which imports bananas and other produce from Central America.

Importers may also try to negotiate lower prices with foreign suppliers, which would reduce the tariff.

How are the tariffs paid?

Most importers employ customs brokers who calculate the tariffs owed based on the goods’ value and where they were exported from. Other factors — like whether a product has components from China — can complicate the tariff calculation.

Payments are made electronically, from the bank accounts of either importers or the brokers, who later recoup the money from their clients. As Mr. Trump has piled on tariffs, some brokers are becoming more cautious and demanding customers pay up quickly.

“With changing tariffs and increased risk, many brokers are tightening their credit policies — asking for upfront payments or requiring funds to be held on account,” said Adam Lewis, a co-founder and president of Clearit, a customs broker.

Where does the money go?

The tariffs end up at the Treasury Department, which also receives taxes and other government fees, and spends the money on things like salaries, weapons and equipment.

What happens if a business pays less than it owes?

Calculating tariffs can be difficult, especially when tariff rates change a lot in a matter of days, as they have recently.

Trade rules allow for some leeway, said Mr. Page, the lawyer. Importers who realize they have made a mistake and inform Customs and Border Protection are usually allowed to pay what they owe, plus interest.

But, Mr. Page said, Mr. Trump’s recent executive orders on metals tariffs were stricter than that. The order said Customs and Border Protection could impose much higher monetary penalties if importers misclassified goods, an approach that, in Mr. Page’s view, defies the law.

“That mandate says, ‘We’re going to hammer you no matter what,’” he said.

Will the new tariffs cause delays?

Customs and Border Protection’s systems are already showing signs of strain.

On Friday, the agency said importers had not been able to submit tariffs owed on certain goods. The glitch appeared to be preventing importers from applying a lower tariff rate on goods that were in transit to the United States before some of Mr. Trump’s new levies took effect.

Customs and Border Protection said it was releasing the goods affected by this problem and allowing importers to submit their customs duties later.

Late Friday, a spokeswoman for the agency said: “There was a brief technical issue that was quickly identified and resolved. It had no impact on cargo flow, and all applicable tariffs were collected during that time.”

“This won’t be the last time that something like this happens,” Mr. Lewis said, adding that there may be backlogs when customs officials do more checks to see if the tariffs on Chinese goods are being paid correctly.

Countries that don’t strike trade deals with the United States by July may face higher tariffs, and Mr. Trump may suddenly decide to introduce new tariffs. Fears of such levies could extend a monthslong rush to get goods into the United States before the new tariffs take effect.

Supply chains have so far handled the higher volumes without major snags.

Trucking activity around Laredo, Texas, one of the busiest border crossings in the United States, was 46 percent higher than it was a year earlier, according to Motive, which gets its data from cameras fitted inside vehicles used by supply chain companies. Local truckers said their networks had not been strained.

At the Port of Long Beach and Port of Los Angeles, trucks took 71 minutes on average to pick up cargo from terminals in the first three months of this year, according to data from the Harbor Trucking Association, a trade group. That was slightly up from 68 minutes in the first three months of last year. In the first quarter of 2022, when the pandemic trade boom caused backlogs at the ports, pickups took an hour and a half.

Danielle Kaye contributed reporting.

The last time the courts seriously weighed the wisdom of breaking up a giant technology company was a quarter-century ago, after Microsoft was found to have illegally stifled competition in personal computer software.

A Federal District Court judge said yes to forcing Microsoft to split in two, separating its monopoly Windows operating system from its Office productivity products and other software. But an appeals court threw out the order, calling the breakup option “a remedy that is imposed only with great caution, in part because its long-term efficacy is rarely certain.”

In a pair of landmark proceedings this month in two Washington courtrooms, the issue of possibly breaking up a big tech company will be on the judicial table again.

In an antitrust trial that began on Monday, the Federal Trade Commission argued that Meta maintained an illegal monopoly in social media through its acquisitions of Instagram and WhatsApp. The agency seeks to force Meta to divest both. Next week at a separate trial, a federal judge will hear arguments from the Justice Department about why the court should break up Google in order to remedy the company’s monopoly in internet search.

“Divestiture can be an entirely acceptable remedy, depending on the severity of the harm,” said William Kovacic, a law professor at George Washington University and a former chairman of the F.T.C. “But it can be risky surgery.”

For generations, the courts have faced the quandary of what action to take in major antitrust cases once a dominant company has been found to have engaged in anticompetitive behavior. In a 1947 Supreme Court ruling, Justice Robert H. Jackson memorably wrote that if a court’s solution did not open the market to competition, the government would have “won a lawsuit and lost a cause.”

But while a court’s ruling is based on examining facts in the past, its remedy looks to the future. The goal is to free up markets rather than hobble them — and create a competitive environment that results in more new ideas, new companies, more innovation and lower prices.

The challenge is taking on new significance as regulators make a major push to rein in the tech giants in a string of antitrust cases objecting to the power they have over communications, commerce and information.

In a different lawsuit against Google, the Justice Department is awaiting a judge’s decision on the company’s dominance in advertising technology. The department has also sued Apple over its tactics to protect its lucrative iPhone franchise. The F.T.C. has sued Amazon, saying the company illegally shielded its monopoly in online retailing from competition.

This wave of antitrust litigation, including appeals, is likely to last for years. And if the government wins any of its cases, a judge could order a breakup — the worst-case outcome for the companies.

History shows that these orders can be effective, antitrust experts said. But the results in improving competition has been mixed.

Standard Oil, an energy giant founded by John D. Rockefeller in 1870, was the defining case of the progressive, trustbusting era of the late 19th and early 20th centuries. The company was broken up by the Supreme Court in 1911, split into 34 entities that had made up the original Standard Oil Trust, which controlled the oil industry’s production, refining, distribution and pricing. While that initially helped competition, over time the trust’s descendants became oil giants of their own, including Exxon Mobil, Chevron and ConocoPhillips.

The breakup of AT&T, in a settlement in 1982, followed a lengthy antitrust suit by the Justice Department, which accused the company of illegally monopolizing the telecommunications market in America. The local phone business was split into seven regional “Baby Bell” companies, and the order opened up the long-distance phone and telephone equipment markets, increasing competition and driving down prices.

In antitrust jargon, a “structural” solution like this generally means a breakup. But there are steps short of a forced sell-off that can shape markets and stimulate competition, antitrust experts said.

In 1969, under pressure from a government antitrust suit accusing it of monopolizing the computer market of its day, IBM unbundled its hardware from software — treating them as separate businesses, sold and priced independently. Software would no longer be “free,” included in the price of a computer. That helped ignite the rise of the commercial software industry, with Microsoft as the biggest winner.

Microsoft avoided a breakup, but its eventual settlement in 2001 contained a prohibition against contracts that had essentially used its Windows monopoly as a club by restricting personal computer makers from distributing the software of upstart rivals. That restraint kept the door open to new competition in browser software and search. Google was the leading beneficiary.

“Those were strong remedies without a breakup that created more competition,” said Fiona Scott Morton, an economics professor at the Yale University School of Management.

The next powerful tech companies to face courtroom scrutiny are Meta and Google.

On Monday, the F.T.C. and Meta, formerly Facebook, presented their opening statements in the U.S. District Court for the District of Columbia. Mark Zuckerberg, the company’s chief executive, then took the stand. The essence of the government’s case is that Facebook vastly overpaid more than a decade ago for Instagram and WhatsApp, to kill them off to protect a lucrative monopoly in social networking.

Meta replied that Instagram and WhatsApp had grown and flourished under its ownership. And, the company argued, there is plenty of competition in the social networking market, including the meteoric rise of TikTok.

Should the government win the Meta case, the likely remedial step, antitrust experts said, would be a court order to sell off Instagram and WhatsApp.

Next week in the same Washington court, Google faces the remedies stage in the lawsuit by the Justice Department and a group of states over its internet search monopoly. In August, Judge Amit P. Mehta found that Google illegally maintained a search monopoly.

To restore competition, the government asked the court to order Google to sell Chrome, its popular web browser, and either spin off Android, its smartphone operating system, or be barred from making its services mandatory on Android phones. Chrome and Android are powerful distribution channels for Google search.

Google has described the government’s list as a “wildly overboard proposal” that “goes miles beyond the court’s decision” and that would harm consumers by offering them inferior products. The company has also said it will appeal.

Tim Wu, a law professor at Columbia University who was a White House adviser on technology and competition policy in the Biden administration, supports breakups in the Google and Meta cases.

“If you want to stir the pot, structural solutions are clean and essentially self-executing — you break it up and walk away,” he said. (Mr. Wu writes for The New York Times’s opinion section.)

But any breakup order would be appealed, and the higher courts today seem to echo the skepticism of the Microsoft era.

In a rare unanimous decision in 2021, the Supreme Court ruled that the National Collegiate Athletic Association could not use its market power to stop payments to student-athletes. It was essentially a wage price-fixing case, decided entirely for the plaintiffs.

Yet Justice Neil M. Gorsuch, writing for the court, digressed to make a broader point about judicial restraint in antitrust matters.

“In short,” he wrote, “judges make for poor ‘central planners’ and should never aspire to the role.”

Stocks inched higher in early trading on Tuesday, as the Trump administration’s chaotic tariff rollout continues to spur volatility in the markets.

The S&P 500 opened up 0.5 percent, and the technology-heavy Nasdaq also gained slightly. President Trump’s whipsawing tariff policies are still driving sentiment on Wall Street, especially in sectors facing the threat of more levies or potential reprieves.

Here’s what else to know:

• Bank stocks rose on Tuesday, as major U.S. lenders reported their latest earnings. Bank of America surpassed Wall Street’s profit and revenue expectations, and its shares rose about 5 percent Tuesday morning. Citigroup’s profits also beat estimates, sending its stock more than 2 percent higher.

• Tariff threats are taking center stage in the pharmaceutical and technology sectors, after the Trump administration on Monday took steps that appeared likely to result in new tariffs on pharma products and semiconductors. Shares in drugmaker Eli Lilly were up slightly on Tuesday morning, while Novartis stock was trading roughly flat. Shares in chip giant Nvidia were nearly 2 percent higher, after the company on Monday said it would invest in artificial intelligence infrastructure in the United States.

• Shares in Boeing, the aviation giant, fell about 1.5 percent on Tuesday following a report from Bloomberg News that China had instructed its airlines to halt deliveries of Boeing planes after the Trump administration imposed steep tariffs on Chinese goods.

• In the auto industry, shares in General Motors, Ford Motor and Stellantis — which jumped on Monday after Mr. Trump signaled that he might offer car companies some relief from tariffs — were mixed on Tuesday morning. Shares in General Motors and Ford both fell more than 1 percent, while Stellantis rose about a half percent. The sector, which is grappling with a 25 percent tariff on imported vehicles, is bracing for new levies on imported car parts.

• The U.S. dollar, long a haven in global financial markets, has been falling against other major currencies. But an index that tracks the currency against a basket of major trading partners stabilized early Tuesday, ending a five-day slide.