Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.) told NBC’s Savannah Guthrie in a Wednesday interview that “nobody knows” if the tax bill will create enough economic growth to negate its cost.

Ryan made the remark on "Today" as the House prepares for a final vote on the tax measure, which outside groups estimate will add $1 billion to the deficit, even accounting for economic growth.

The Speaker and other Republicans have suggested those scores underestimate the lift that the economy will receive from the tax bill, a point Guthrie pressed with Ryan in Wednesday's interview.

“Are you saying that the growth you’re going to get from this tax cut will equal the amount it would cost on the deficit side so that it’s a wash, so that you’re not adding to the deficit at all?” she asked.

“Nobody knows the answer to that question because that’s in the future,” he responded. “But what we do know is that this will increase economic growth … You have to get faster economic growth so that people can get ahead in America; that’s what we’re doing.”

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The Joint Committee on Taxation estimates the bill would add $1.46 trillion to the deficit over the next decade before factoring in economic growth.

The nonpartisan Committee for a Responsible Budget in a separate report warned that the cost could be higher if tax provisions set to expire in the bill are instead extended — something Ryan has predicted will happen.

If lower tax rates for individuals and families are extended and not allowed to expire in 2025, the bill would add $2 trillion to $2.2 trillion to the deficit over the next decade, the report said.

The conservative Tax Foundation estimated the bill would add $1.4 trillion to the budget deficit over the next decade if the entire tax plan was made permanent. That estimate took into account faster economic growth under the plan.

Ryan said that Congress also needs to control spending, but that the economic growth from the tax bill was key to boosting the economy.

“We’ve got to control our spending, that — we have more work to do, we clearly have to go after spending control,” he said.

Both the House and Senate voted to pass the bill, but the House will have to vote again on Wednesday after the Senate ruled that two provisions in the bill did not comply with budget rules.