7bn were inbound and 11bn were outbound.
Mobile messaging platform WhatsApp is – ironically – a firm of few words, posting just a handful of tweets each month, while it's press office is also rather barren.
However, the company took to Twitter to reveal it processed a record 18 billion messages on New Year's Eve, with seven billion of those inbound and 11 billion outbound.
When questioned on the difference between inbound and outbound messages by a follower, WhatsApp said: "difference in inbound vs. outbound is due to group chat. sending one msg into group chat of 10 people is 1:10 inbound:outbound."
The milestone comes following the previous record of ten billion messages in one day back in August (4bn inbound, 6bn outbound), while it was processing 1bn a day back in November 2011.
This time last month it was rumoured that Facebook was eyeing a WhatsApp buyout, though both firms quickly played down the whispers.