She would also be required to pay interest on the student loans she took out to complete a master’s degree at Temple University. While the loan payments are deferred during her doctoral program, the interest on those loans continues to accrue and she would no longer be able to deduct portions of that cost once the payments restart.

“I’m older than many of my classmates,” said Ms. Vause, 39. “I have no parental support. I’m supporting myself, and I’m halfway through my program. To suddenly make these changes, well, the bill would not allow me to complete my degree.”

Even people with financial resources may find their careful fiscal planning upended. Two years ago, Mr. Kepley, who uses a power-assisted wheelchair, moved into a retirement community so that he and his wife would be cared for should their health deteriorate. The community requires a hefty entry fee and a monthly payment, which gives residents lifelong access to an independent living center, nursing home and an Alzheimer’s unit.

Mr. Kepley said he was initially deterred by the cost, but friends who had already made the move explained that it was basically an insurance policy against future health problems and that he could deduct some of the fee as a prepaid medical expense.

“That’s the advantage: That ahead of time, I can afford this and know that if I progress in these various phases, I will not have to worry about paying for it,” Mr. Kepley said. “The tax benefit was a factor in my decision.”

Mr. Kaplan said there was a certain irony that the bill would punish people like Mr. Kepley, who were trying to avoid running out of money and winding up on Medicaid.

“They were the ones doing the fiscal personal responsibility thing, and then they turn around and say we’re changing policy that’s been in place for decades,” he said. The medical expense deduction, he added, “is a huge financial factor in the sense of making the cost work.”