Democrats are divided on how quickly they want to move this bill through Congress. Some progressive lawmakers are advocating for a vote in the House as soon as this week. Moderate Democrats, including Senator Joe Manchin of West Virginia, have said the negotiations should not be rushed and could extend into 2022. Many congressional experts expect the bill will pass just shortly before the Christmas holiday, a date that has historically served as a motivating deadline for lawmakers to reach a deal so that they can go home to celebrate with their families.

For advisers executing sophisticated tax-avoidance strategies, the details matter. So does exactly when changes get implemented. The White House’s plan said it would hike capital gains rates starting after the date it was announced—in late April—a retroactive increase that would have meant rich investors owe almost twice as much on transactions executed in May than in March.

Then the House proposal moved its more modest capital gains hike to start after Sept. 13. Other tax provisions in the bill had different effective dates, including the day they become law and the end of the year. There’s no guarantee any of those dates will remain in final legislation.

Clarity on the timing of tax hikes would make them easier to avoid. If investors know taxes are going up in the future, they can rush to sell now.

“It seems like they’re trying to create paralysis, so people don’t do anything,” said Jeremiah Barlow, head of family wealth services at Mercer Advisors. He thinks there’s a 50-50 chance that the effective date on the capital gains hike could slip to later in the year as negotiations over the package stretch onward.

The question of effective dates is especially important for people already in the midst of large transactions that would trigger capital gains. For clients about to sell a business, for example, the best advice may be to hurry up and hope your transaction falls under the lower tax rate, Barlow said. “Either the rate is going to go up, or you’re going to get the windfall of it being lower.”

The threat of higher taxes is pushing some rich Americans to make moves. Owners of multi-billion-dollar businesses have sped up plans to sell them off, advisers say, hoping the deals are completed in time to avoid the tax hikes. Other wealthy investors are exploring niche strategies, including one called private placement life insurance, that are designed to avoid taxes on future gains.

In some cases, haste could be a mistake. Both the White House and House legislation would hike the top ordinary rate back to the pre-2018 level of 39.6%, up from 37%, at the end of the year. The House bill would also add a 3% surcharge on incomes above $5 million next year. If those and other tax hikes take effect in 2022, it might be tempting to try to pay more to the IRS this year in ways that would lower future years’ tax bills.

Strategies for doing that include speeding up business income, deferring charitable contributions and other deductions to future years, or moving money from traditional IRAs to tax-free Roth accounts.

But all these moves could backfire. Taxes might not rise as much as expected—or might not happen at all. The House bill includes a $10-million cap on Roth IRAs, and Democrats have previously discussed limiting the total size of wealthy taxpayers’ deductions.