Australian shoppers are tipped to spend more than $15 billion in this year's post-Christmas sales.
Australian Retailers Association executive director Russell Zimmerman said indications were this year's sales would top the $14.8 billion shoppers spent last year between December 26 and January 15.
WA is expected to account for less than $2 billion of the nation's spending spree.
The post-Christmas sales spending is on top of the $42.1 billion shoppers are expected to spend in the lead-up to Christmas Day, according to ARA forecasts.
WA is expected to account for about $5 billion.
Mr Zimmerman said WA's retail sector was slowing down because of the effects of the mining industry downturn.
He said that more stores were opting for pre-Christmas sales, but there was no indication those sales were cannibalising the traditional post-Christmas sales.
"Far from it - in actual fact they are seen as being very important sales," he said.
"When you get to Boxing Day they're just as big as ever. It's an interesting phenomenon."
Last year there was a 300 per cent surge in domestic online Boxing Day sales and Mr Zimmerman said he expected online sales to continue to grow strongly, albeit still off a very low base.
As was the case last year, some brick-and-mortar retailers are expected to start their online sales as early as Christmas Eve.
In Perth, Myer's visual merchandise manager Troy McKnight said Boxing Day was the group's biggest day of the year and usually had a "celebration atmosphere".
"Most people are generally in a good mood," he said. "People have come in with their money or their gift cards that they've got for Christmas.
"Rarely do we get Christmas returns on Boxing Day - they're here to shop."
He said that in his 11 years with Myer he had seen over-eager shoppers run into fixtures or go the wrong way on an escalator.
Many years ago a male shopper jumped from one floor to another to pick up a cheap television, he said.
Retailers can trade from 8am to 6pm on Boxing Day this year after the State Government extended Sunday trading hours.
Ahead of Christmas, people are already getting their spending mojo back.
The Commonwealth Bank's business sales indicator, which tracks spending through the bank's credit and debit cards, showed spending was up last month, the 15th consecutive month of growth.