Canadians could be poised to spend almost $1 billion on their debit cards tomorrow, making Dec. 23 the busiest shopping day of the year with 19 million purchases, Interac says.

The payment processing company said that last year, on the Tuesday before Christmas (which was on Thursday), Canadians spent $993,390,588.84 on their debit cards, with more than 19.6 million different transactions.

That compares with a normal day this time of year, which would still be strong but not as much. The company says Canadians spent $680 million this past Wednesday, Dec. 16, across Interac's network.

Retail sales always peak during the month between U.S. Thanksgiving (at the end of November) and Jan. 1, driven by holiday spending. But this year could be poised to be even bigger than usual.

More than one-third of money spent was devoted to grocery purchases, likely in preparation for a Christmas Day feast, Interac's senior manager of communications Teri Murphy said.

Purchases at discount stores, as well as beer, wine and spirits, round out the most common purchases.