It's no surprise to anyone that December is the biggest sales month for Australian supermarkets, but it may come as a shock to learn that some products have more than a tenth of their yearly sales in the week before Christmas.

Figures from research company IRI from more than 13,000 households, as well as supermarket scan data, show that 23.5 per cent of larger ham joint annual sales are made in the week before Christmas, as well as 12.2 per cent of turkeys.

Other products such as boxes of chocolate, custard, ice, and batteries see substantial amounts of their total yearly sale in the week from December 17 to 24.

Shoppers spend 14 per cent more than average per shopping trip in the final week before Christmas, which affects which supermarket is more successful for the year.