Gatwick achieved the busiest month in its history in August with more than 4.53 million passengers using the airport.
This represented a 3.7% increase on the same month in 2014 and means that Gatwick has seen 30 months of consecutive growth.
A total of 39.5 million passengers have been handled in the last 12 month, up 6% year-on-year.
Gatwick chief executive, Stewart Wingate, said: “Airports Commission analysis predicted Gatwick would reach 40 million annual passengers in 2024 yet, in August 2015, we reached the 39.5 million passengers mark.
“We are in touching distance of 40 million and on track to reach this milestone within a matter of weeks.
“This is more evidence of the flaws in the Airports Commission and we will continue to make our case to government as it approaches a decision. Gatwick remains the best and most deliverable option to actually deliver the runway that the UK needs.”
He added: “While we are already at capacity at peak times, we continue to make substantial investment in the airport to allow us to continue to grow.
“This week, we reached the half-way point in our project to renew and revitalise our North Terminal which is part of our £2 billion transformation programme.
“The fact remains, however, that the UK needs extra runway capacity and Gatwick can deliver this more simply, quicker, and with no burden passed on to the tax-payer.”
Passengers flying to the US and Canada rose by 9.5% in the month with Orlando seeing the biggest long-haul increase, rising by 13.3%.
European destinations saw growth of 5.5%, the equivalent to more than 167,000 extra passengers, with Madrid seeing the biggest increase.