On the other side, the receiving spouse, who would have paid $15,416 in taxes in a divorce settled last year, was able to keep the entire $100,000 tax-free this year.

The difference grows as income grows. Mr. Richards ran a similar projection with someone earning $2 million and paying out $400,000 in alimony. Because of the lost deduction, that divorce cost at least $120,000 more this year.

That increase, divorce lawyers said, has already slowed down negotiations. Peter R. Stambleck, a partner at the family law firm Aronson Mayefsky & Sloan, said that what he called “the legal spread where the government was eating the difference” in taxes often helped the two sides come to an agreement.

One way the wealthiest are looking to get around this change is by setting up trusts for their former spouses that will pay out income equivalent to the alimony but without the tax burden. There’s a bit of a science to setting up these entities, called grantor trusts, and an art to persuading the receiving spouse to pay taxes on the money paid out.

The trusts need to be funded with assets that will generate income as a substitute to the alimony payment and established after the divorce has been finalized, or else the spouse funding it will be responsible for the taxes, said Eugene Pollingue Jr., a partner at Saul Ewing Arnstein & Lehr. “It’s not alimony,” he said. “It’s a property settlement, and that’s tax-free.”

To sell it to the spouse who will then have to pay taxes on the distribution, Mr. Pollingue said, the trust ensures payments continue even if the paying spouse dies — alimony stops at death — and whatever is left when the receiving spouse dies can go to heirs.

Some accountants caution that the technique is too aggressive.

“Let’s say you created a trust for the benefit of a spouse, and you’re guaranteeing $2,000 a month,” said Carrie Baron, a certified public accountant and co-founder of the accounting firm Baron Strohmenger. “The I.R.S. could say that’s just disguised alimony.”