Sir Michael Cullen has earned more than $84k for his part-time work as chair of the Tax Working Group.

The group released its final report on February 21 recommending a capital gains tax be applied to gains from residential rental properties, all land and buildings, business assets, intangible property and shares.

But Cullen has controversially been kept on beyond the report's release to answer queries about the report.

In response to a question from National's finance spokeswoman Amy Adams, finance minister Grant Robertson said Sir Michael Cullen had been paid $84,115.05 as at March 6 2019.

"This includes reimbursement of expenses incurred, as well as appropriate remuneration for the chair's time."

Robertson said some invoicing for the period to March 6 was still to be processed.

Cullen is being paid around $1000 a day on a pro-rata basis depending on how many hours he does.

Cullen, who was the former finance minister between 1999 and 2008, was appointed to head up the group in November 2017.

National has claimed the nature of Cullen's pay means the amount covers less than four months of actual work.

Robertson said the Tax Working Group members and chair were paid as a group four, Level one body under the Cabinet Fees Framework.

The Government has said it will respond to the Tax Working Group report in April.