The bill is likely to change significantly in coming days. On Monday evening, the House’s tax-writing Ways and Means Committee began the formal process of reviewing the bill, which could involve dozens of amendments, some of them substantial. The bill, which the House could pass as early as this week, is likely to change further in the Senate, where procedural rules place practical limits on how much the plan can add to the federal deficit.

The Times analysis looks at the direct effect of the tax changes on Americans’ incomes and does not account for changes in economic growth that Republicans say will amplify the impact of the tax cut and deliver higher wages to Americans across the income spectrum. Economic models disagree about the size of those effects, but generally agree they would be smaller in the initial years after a bill was passed since the tax cuts would take a while to filter throughout the economy.

Still, Republican leaders in Congress and the White House haven’t just argued that the bill would have broader economic advantages. Rather, they have repeatedly described it as a tax cut for middle-class families.

“This whole tax reform is designed for the middle-class family that’s working so hard, for that Main Street business that’s working so hard,” Representative Kevin Brady, Republican of Texas and chairman of the House Ways and Means Committee, said on MSNBC on Thursday. Senator Mitch McConnell of Kentucky, the majority leader, went further, telling the MSNBC host Hugh Hewitt over the weekend that “nobody in the middle class is going to get a tax increase” under the bill.

Few independent economists find evidence to support that claim. Analyses published since the plan was introduced last week have consistently found that some middle-class families would see their taxes go up immediately, compared with existing law. One such analysis, from the Institute on Taxation and Economic Policy, found that 8 percent of middle-income earners would pay more in 2018 — and 21 percent in 2027 — with upper-middle-class taxpayers more likely to see their taxes rise.