The index revealed online sales at domestic "daily sales" stores continued to fall and when they were excluded domestic sales were up 9 per cent.
Groceries and liquor, furniture, sport and camping equipment, toys and games, entertainment media and garden supplies were the biggest areas of growth showing double digit growth compared to December 2012.
The growth in online sales is an ongoing trend.
Comparing month on month figures shows online sales for October up 11 per cent, November up 12 per cent and December up 13 per cent on the same months in 2012.
International online purchases rose from 17 per cent up in October to 21 per cent up in November to 24 per cent up in December.
The index also looks more closely at retail activity on Christmas Day and Boxing Day revealing shopping on those days has surged.
For Christmas Day it was up 13 per cent compared to 2012 and up 17 per cent for Boxing Day.
The research notes that online spending on Christmas and Boxing Days was lower than what Kiwis typically spend online each day throughout the year.
"We suspect this is partly because many people's focus is elsewhere over Christmas, and partly because people are very accustomed to attending Boxing Day sales at physical stores.
"It will be interesting to see what changes in spending patterns unfold as New Zealanders' online shopping habits continue to evolve."
It also found online shopping on Christmas Day accounted for over 25 per cent of all New Zealand retail sales on December 25 and said that could be put down to most physical stores being closed.
It noted that close to 60 per cent of the online shopping on Christmas Day was done at overseas sites.
