Heathrow said on Tuesday that it had its busiest January on record, with more than 6.3 million passengers travelling through the airport.
This marked a 5% increase on the same month a year ago. The airport also said it was the eleventh month in a row that it averaged more than 200,000 passengers a day, with transatlantic travel a key contributor.
More than 1.2m passengers travelled between the UK and US, up 8% on 2024.
The airport welcomed Chancellor Rachel Reeves' recent show of support for a third runway.
It said that to successfully deliver this project at pace will require policy changes, including on airspace modernisation, planning policy reform and changes to the regulatory regime. Heathrow said it was working with its stakeholders to finalise plans and will submit its proposal to Government by the summer.
Chief executive officer Thomas Woldbye said: "2025 has started how we mean to go on - serving record breaking passenger numbers and delivering trade and investment across the whole of the UK.
"To ensure we continue on this upwards trajectory, the Government has signalled their support for an expanded Heathrow. We'll now work with Ministers to progress the necessary policy changes required to advance our growth plans."