I should have answered tax question: Bowen

Shadow Treasurer Chris Bowen knows he should have answered Alan Jones' questions about the tax-free threshold, and admits his on-air stumble was not the best television viewing.

The Labor MP faced an uncomfortable grilling from the talk show host during a Tuesday night interview on Sky News, where he refused to cite the threshold figure.

Mr Bowen on Wednesday fronted reporters to explain the gaffe, and was again asked to nominate the amount at which people begin to pay tax.

"The tax-free threshold is $18,200, which is what I should have said last night," Mr Bowen said in Sydney.

"I should have answered the question. I didn't want to get into a long discussion about what various thresholds are."

A contrite Mr Bowen acknowledged it was not the best look for a shadow treasurer to refuse to answer the question, but denied it would impact on his economic credibility.

Opposition Leader Bill Shorten said he "absolutely" still had confidence in his treasury spokesman, attributing the stumble to a long day.

"Chris knows what he got wrong last night. He also knows the tax-free threshold," he told reporters in Melbourne.

"The person I don't have confidence in, and I think I speak for millions of Australians, is Joe Hockey."

Liberal frontbencher Simon Birmingham said everybody made mistakes.

"But you do expect that the shadow treasurer will at least in ball-park terms - if not in the precise dollars - be able to talk about the tax rates, the tax-free threshold," Senator Birmingham told Sky News.

Labor MP Ed Husic defended his colleague's performance, saying government was not about getting a sash for the best rote learner.

"Does anyone seriously believe if later today Treasurer Joe Hockey is given a pop quiz on the tax scales and he passes that that means he's going to be able to frame a good budget?" Mr Husic asked.