The Government's maths skills have come under fire over the alleged economic cost of "Mondayising" public holidays.
Labour believe the Prime Minister has overestimated the cost of giving employees a day off for every Waitangi Day and Anzac day that falls on a Saturday or Sunday - a twice in every seven years occurrence.
Dunedin North MP David Clark said official records show the Government has focused on counting the cost of legislative change without considering the potential economic benefits for employers and the boost to the domestic tourism market.
He said the calculations used to justify National's stance that the Holidays (Full Recognition of Waitangi Day and Anzac Day) Amendment Bill would stall productivity, are misleading and "overstated".
He said the calculations include the hours worked by self-employed workers who are not included to the Holiday's Act, while ignoring the benefits of rested employees and the boost to the domestic tourism market.
"That is like counting the downsides of a mortgage without recognising the fact that you own a house," Clark said.
"As well, no account has been taken of the fact that employers can make changes to the way they operate their businesses and who works on which days, further reducing costs."
The Labour MP is behind the bill that was drawn from the private's member ballot to go before Parliament in February.
It would see Waitangi Day and Anzac day continued to be celebrated on April 25 and February 6 with a public holiday given on the following Monday.
"If the Government stuck to the facts it would see the Bill is just plain common sense."
"Kiwis are entitled to 11 statutory days off each year. Hopefully they will be entitled to a day off for each and every one of them before the year is out," Clark said.