The $1.5 trillion federal tax-cut bill awaiting President Donald Trump’s signature will cause a de facto state tax hike for some Coloradans, state budget forecasters said Wednesday, news that could be viewed as an unexpected Christmas gift for state budget writers — and a lump of coal for those who will foot the bill.

The seemingly contradictory result could generate between $196 million and $340 million next fiscal year, an unexpected windfall that immediately raised hopes for more transportation funding in the 2018-19 state budget.

Aside from the tax bill fallout, the two quarterly revenue forecasts released Wednesday by the Colorado Legislative Council and Gov. John Hickenlooper’s office were largely in line with the most recent forecasts. Both forecasts, released in September, expect the Colorado economy to continue growing steadily, albeit at a slow pace, due to the state’s tight labor market and already low unemployment rate.

The explanation for the state tax jump comes down to how the state calculates its income taxes:

State income taxes are a flat 4.63 percent of federal taxable income. And while the Republican tax bill would cut federal income taxes, it also eliminates or caps a number of deductions, resulting in a broader tax base. The net result at a federal level is lower taxes for most individuals, because the drop in tax rates will more than offset the lost deductions in most cases.

But in Colorado, state income tax collections would grow. That’s because the tax rate of 4.63 percent won’t change, while the base — the amount of income that is considered taxable — grows because of fewer deductions.

“In broadening the federal tax base, we’re broadening the state tax base, while maintaining constant tax rates under current law,” Kate Watkins, the chief economist for the Colorado Legislative Council, told the Joint Budget Committee in Wednesday’s briefing. “So the result in this is an increase in tax revenue, which may seem counterintuitive, in that we’re hearing a lot about federal tax revenue reductions and federal tax cuts.”

The impacts of tax reform vary wildly from person to person. But generally, those who currently claim deductions and exemptions that are being eliminated could end up paying more in state taxes.

It was not immediately clear from Wednesday’s forecasts who would bear the brunt of the increase. Two of the mostly hotly contested changes to deductions would only impact wealthy Coloradans. Under the final bill, state and local tax deductions will be capped at $10,000, while the mortgage interest deduction will be capped at $750,000.

For Coloradans who don’t use these or other itemized deductions that were eliminated, their state tax bill could go up or down depending on how many people are in their household.

The standard deduction was nearly doubled, which represents a cut to state and federal taxable income. But the personal exemption was eliminated, which means higher taxes for larger families. At the federal level, this is offset somewhat by an expanded child tax credit, but that wouldn’t apply to someone’s state taxable income.

Colorado is not alone. A Tax Foundation analysis found that most states would have a broader tax base as a result of the federal tax bill, “forcing states to decide whether to keep the additional revenue to grow government, cut rates to avoid an automatic tax increase or use the broader base to help pay down broader tax reform.”

In Colorado, the political winds in both parties are pointing toward spending it. The question that will persist throughout the next legislative session is where the money will go.

Hickenlooper’s office promised to return with an updated budget proposal in January that would spend the extra money on education and transportation, while using the rest to build up the state’s reserves.

Rep. Millie Hamner, D-Dillon, the top lawmaker on the powerful Joint Budget Committee, pointed to those and other pressing matters, such as the state’s child health insurance program, whose federal funding is set to run out, and an expected decline in severance tax revenues, which help fund public projects at the local level, among other things.

“There is no shortage of unmet needs,” she said in a statement. “We will be looking to balance Colorado’s many competing statewide priorities in the coming months.”

For top Republicans and business groups, the reaction was swift and unequivocal Wednesday:

“Roads are our top priority, and there is no reason why nearly all of this new revenue should not go to widening highways and expanding primary arteries,” House Minority Leader Patrick Neville, R-Castle Rock, said in a statement.

“Colorado is growing and the traffic situation across the state’s most important highways and byways is reaching a crisis point,” said Mike Kopp, the CEO of Colorado Concern, an alliance of state business executives. “There will be time for a conversation about new revenue and ballot initiatives in the future, but the job at hand is clear – the General Assembly can and must make a significant financial commitment from the tax dollars the state already collects, and do it this year.”

If the federal tax bill is signed into law as expected, the Legislative Council forecast projected an extra $35 million this fiscal year, and $196 million in 2018-19.

The governor’s office was even more bullish, predicting anywhere from $120 million to $150 million this fiscal year, plus another $270 million to $340 million in 2018-19 due to the tax code changes.

In terms of the general fund, both forecasts expect revenue to grow, even excluding the potential effects of federal tax reform. The Legislative Council expects state revenue to grow by $747.9 million, or 6.7 percent, in 2018-19, up from $666 million in the prior forecast in September.

The governor’s forecast for next year is slightly more conservative, projecting general fund revenue to grow by $742 million, up from $636 million in the prior forecast.

However, revenue in the current fiscal year could jump by $179 million over the prior forecast, said Henry Sobanet, the governor’s budget director. He believes investors will begin claiming more capital gains on their income taxes after months of waiting for federal tax reform to pass.