London Heathrow Airport is one of the world’s busiest airports. It handled approximately 84.5 million passengers in 2025, and, in the first half of 2026, around 40 million passengers passed through its terminals. According to OAG, Heathrow is the world’s second-busiest international airport by scheduled capacity in September 2026, behind Dubai International Airport. More than 4.3 million seats are scheduled at the airport this month.

For much of the past three decades, Heathrow has also been Europe’s busiest airport. It held the title from 1996 to 2019 before the COVID-19 pandemic disrupted international aviation. The airport returned to the top of the European rankings in 2023. However, it has now lost that position to another European airport. Heathrow expects to handle 83.6 million passengers in 2026, which would be a 1.1% decline from its record 2025 figure.

Istanbul Airport Takes The Lead

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Istanbul Airport has taken the position as Europe’s busiest airport by passenger numbers after overtaking London Heathrow in July. According to Airports Council International, a total of 8.15 million passengers passed through the Turkish hub during the month. Heathrow, meanwhile, recorded 7.9 million passengers, almost 300,000 fewer travelers in a single month.

Overall, Heathrow’s July passenger traffic was 1.5% lower than in the same month last year. The biggest decline came on Middle East routes, where passenger numbers fell 20.2% year-on-year. The ongoing Iran-US conflict has disrupted travel patterns across the region and affected demand for flights between Heathrow and Middle Eastern destinations.

Istanbul, on the other hand, recorded a different trend in July. Passenger traffic at the Turkish airport increased by 2.3% from the same month last year. Indeed, the competition between the two airports has been close for some time. Istanbul finished 2025 only around 40,000 passengers behind Heathrow.

It then started 2026 ahead of the British airport, with 6.9 million passengers in January compared with Heathrow’s 6.5 million. Heathrow regained the lead as the year progressed, but the margin remained extremely small. Just 3,012 passengers separated the airports in May. At the end of June, Heathrow had handled 40 million passengers compared with 39.84 million at Istanbul. A month later, Istanbul had finally moved ahead.

Istanbul Airport’s Growth Has Been Rapid Since 2019

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Indeed, Istanbul Airport has expanded at an impressive pace since it opened in 2019. Within months, all passenger flight operations had moved from Atatürk Airport to the new facility. The airport quickly developed into a major global hub. It ranked as the world’s 28th-busiest airport by passenger numbers in 2019, according to ACI. By 2025, it had climbed to eighth place.

Istanbul Airport now connects to more than 330 destinations across over 120 countries. A large share of the traffic comes from passengers who use the airport to connect between international destinations rather than ending their journeys in Istanbul. Notably, the airport was named the world’s most connected airport in ACI’s 2025 Airport Industry Connectivity Report.

The scale of that operation is already visible in its daily traffic. On July 27, 2025, more than 272,000 passengers passed through Istanbul Airport, setting a new daily record for a European airport. A total of 134,893 passengers arrived that day and another 137,239 departed. As noted previously, the airport has continued to see strong traffic this year. In the first seven months of 2026, Istanbul Airport handled 249,520 aircraft movements.

This included 98,158 domestic flights and 101,160 international flights. Passenger traffic also remained strong in July, with 10.48 million domestic passengers and 16.31 million international passengers passing through the airport. July alone saw 50,748 aircraft movements at Istanbul Airport. Domestic flights accounted for 12,190 of those movements, while international flights accounted for 38,558.

Turkish Airlines Is Driving Istanbul Airport’s Growth

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Istanbul’s case for becoming one of the world’s busiest airports is closely tied to the growth of Turkish Airlines. Last year, the carrier transported about 92.6 million passengers across its network, an 8.8% increase from the previous year. In the first seven months of 2026, it has already carried a further 54 million passengers, which is almost 6% more than during the same period last year.

If that pace of growth continues over the next decade, Istanbul Airport could be handling between 150 million and 160 million passengers a year by 2036. The bigger question is whether Turkish Airlines and the airport itself can support that level of expansion. The airline’s original centennial strategy called for more than 170 million annual passengers and a fleet of more than 800 aircraft by 2033. That would require annual growth of around 6%.

Turkish Airlines already has a substantial pipeline of new aircraft to support its plans. The airline committed to 355 Airbus aircraft in 2023, including 230 firm orders and 125 purchase rights. It later agreed to acquire up to 75 Boeing 787-9 and 787-10 aircraft and up to 150 Boeing 737 MAX jets.

The Dreamliners are scheduled for delivery between 2029 and 2034. The airline is also reportedly considering a further order for the Boeing 777-9 or Airbus A350-1000. Should the airline achieve the target of 6% growth annually, Istanbul Airport could easily move beyond 150 million passengers a year.

Heathrow Wants A Third Runway To Support Future Growth

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Of course, there is no guarantee that Istanbul Airport will finish 2026 ahead of Heathrow. The final result will depend on how passenger traffic develops over the rest of the year. Even if Istanbul does finish ahead, one year would not be enough to show that it has permanently taken Heathrow’s place at the top of the European rankings. The bigger story may be what is happening behind the passenger figures.

For decades, Heathrow has remained one of Europe’s leading airports despite operating with just two runways. Those runways now operate close to their maximum capacity, which has left the airport with limited room to handle further growth. Heathrow has therefore been seeking approval for a third runway for years. In a statement following the July figures, Heathrow said that “the case for expansion has never been clearer.”

The proposed expansion would eventually increase Heathrow’s annual capacity from just under 85 million passengers to around 150 million. The UK government has backed plans for a third runway, but the project is not expected to be completed until at least 2035. Heathrow has continued to argue that expansion is needed to protect its position as the UK’s main international hub.

As reported by The Guardian, its Chief Executive, Thomas Woldbye, said expansion would “help ensure the UK remains home to Europe’s leading hub.” For now, despite the recent dip in passenger traffic, Heathrow remains a very important airport. Several airlines have started serving the airport this year, including ITA Airways, Alaska Airlines and Riyadh Air. Heathrow’s long-term position will therefore depend in part on whether it can add the capacity needed to accommodate future demand.

Istanbul Airport Will Soon Have Four Runways

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Istanbul Airport is also preparing to add more runway capacity. Turkey’s Ministry of Transport and Infrastructure says construction of the airport’s fourth main runway is nearing completion. Operations are expected to begin in the final quarter of 2026 after technical testing. That would put Istanbul much closer to adding new capacity than Heathrow, which is still working towards a third runway. The new east-west runway is 2,820 meters (9,250 feet) long and 45 meters wide.

Istanbul Airport has already become the first airport in Europe to operate three independent runways simultaneously. The new runway, alongside other current investments, is expected to increase the airport’s annual passenger capacity from 90 million to 120 million. The airport’s long-term master plan also targets a capacity of up to 200 million passengers a year. Istanbul Airport Chief Executive Selahattin Bilgen described the fourth runway as “a significant milestone” for the airport.

He said its three independent runways have allowed the airport to overcome some of the capacity constraints faced by other major global hubs. Bilgen added that “with the addition of our fourth runway, which is set to become operational by the end of this year, we aim to take this growth even further by increasing the capacity we provide to airlines and passengers while elevating the quality of our services to the next level.”

The Race Between Istanbul & Heathrow Is Not Over

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For years, Heathrow held the position as Europe’s busiest airport by passenger numbers. That position has now been challenged by Istanbul Airport, which has seen consistent growth since it opened and benefited from strong demand across its growing network. Heathrow’s passenger traffic has also come under pressure this year as geopolitical events affected some of its international markets.

Both airports have plans to expand their capacity further. Heathrow’s proposed third runway could eventually allow the British airport to handle around 150 million passengers a year, but that additional capacity remains years away. Istanbul, meanwhile, is already preparing to put its fourth runway into operation within months. Its annual passenger capacity is expected to rise from 90 million to 120 million as a result of the new runway and other investments.

That makes the next few years particularly interesting for both airports. Heathrow has the potential to regain its position once it can add more runway capacity, but Istanbul is continuing to grow and expand its infrastructure at the same time. For now, Istanbul has taken the lead. Whether it can hold onto it will depend on how quickly passenger demand grows at both airports and how soon their expansion plans become reality. We will just have to wait and see.