A party spokesman said Labour saw a real spike in online donations when Jacinda Ardern became leader before the 2017 election.
"This election our small dollar fundraising played a more important role than ever in funding the campaign," he said.
The average online donation was $34 and more than $1m was raised online this year.
The spokesman put the success down to the incredible response by people to Prime Minister Jacinda Ardern and the direction she and the party are taking New Zealand.
A National Party spokesman said it does not comment about donations to the party.
Campaign expenses from the 2017 election show Labour outspent National, albeit by a small amount.
Labour spent $2.58m, including public funding of $1.1m. National spent $2.54m, including public funding of $1.37m.
Political parties have until March 17 to return their election and referendum expenses for the 2020 election. Electorate candidate returns of election expenses and donations are due on February 17.
The expenses are usually made public within a week of the return dates.