Mr. Bennet would expand the child tax credit. Mr. Brown has one bill to increase the size of the earned-income tax credit, which would cost $159 billion for one year, and another to expand both that credit and the child tax credit, at a cost of $99 billion. Ms. Harris would also increase the earned-income tax credit, while adding an additional credit on top of it. Mr. Booker would replace the earned-income tax credit with a far more generous credit for workers; his plan would run $251 billion.

All of the credits would be refundable, meaning workers could claim them — and receive checks from the federal government — even if they didn’t have to pay income taxes. As a result, each of the plans would deliver a benefit of at least $1,000 a year to the poorest 20 percent of workers, the Institute on Taxation and Economic Policy found.

Mr. Booker’s and Ms. Harris’s plans would offer the most to that group: an average boost of $2,500 under his proposal and $2,450 under hers, which is about a 17 percent income gain for a typical worker in that group.

Mr. Trump’s tax cuts delivered an average gain of $60 for workers in that group, the study found.

The analysis examined five Democratic plans that focus on tax cuts for the middle class. It does not include some candidate plans designed to raise revenue through taxes on the wealthy, such as Senator Elizabeth Warren’s proposed wealth tax, though the institute plans more analyses as the presidential race progresses.

The proposals from Ms. Harris and Mr. Booker, and one of Mr. Brown’s plans, would deliver larger benefits for taxpayers in the middle of the income distribution than Mr. Trump’s cuts did, the analysis found. The less expensive of Mr. Brown’s plans would deliver smaller benefits, as would Mr. Bennet’s, though both plans would give a larger share of their overall windfalls to the middle class than Mr. Trump’s did.

Ms. Harris has said she would repeal the Trump tax cuts. A spokesman for her campaign, Ian Sams, said Tuesday that the new analysis confirmed that her plan was “a complete 180 from Trump’s disastrous tax bill — it helps working families make ends meet each month and lifts up those living in poverty, not the very rich and big corporations.”

Mr. Bennet’s plan would benefit only low- and middle-income families with children. Other plans would benefit workers with or without children. Ms. Harris’s plan would give the largest benefits to married workers with children. Mr. Booker’s plan would give its largest benefits to married workers without children.

All of the plans would deliver an outsize portion of their benefits, as a share of all taxpayers, to black and Latino families, because those workers disproportionately fall in the bottom 60 percent of taxpayers by income. Mr. Trump’s tax cuts, by favoring higher-income taxpayers, delivered an outsize share of their benefits to white and Asian taxpayers.