The typical value of a purchase made using a debit card was £43.70 in June, 96 pence less than it was 12 months earlier, according to data from the UK Cards Association.
Meanwhile, the average value of a payment made by credit card has fallen by £2.71 year-on-year to £60.13.
The association said the volume of purchases using cards was on the rise. The number of purchases grew 9.2 per cent year-on-year in June, to 993 million in total across the month.
But because cards are increasingly being used for low-value purchases, the overall value of spending on cards has increased more slowly than the volume.
Richard Koch, head of policy at the UK Cards Association, said: "The use of contactless cards for lower, everyday sums is partly behind this trend."