Pak'nSave has come out cheapest in a survey of supermarkets.
Countdown came second and New World third, according to Consumer's price survey released today.
Shoppers bought 30 top-selling products on the same day from supermarkets in Auckland, Hamilton, Tauranga, Wellington, Christchurch and Dunedin.
The number of products on special at Countdown gave it the edge over New World, Consumer NZ chief executive Sue Chetwin said.
"While special offers can reduce the weekly grocery bill, if an item is routinely discounted, you have to ask how special is the special price?"
To track the regularity of specials Consumer checked online prices of 10 items at Countdown and New World Thorndon over 13 weeks.
Most items were regularly discounted, she said.
A block of chocolate was on special for 11 of the weeks at New World and eight at Countdown, and a block of cheese seven weeks at New World and six at Countdown.
The results lent support for regular price monitoring, Ms Chetwin said.
"Stores tempting customers with price promotions must be offering a genuine deal. If they're not, they risk misleading consumers about the savings available and breaching the Fair Trading Act."