Connecting flights at Heathrow: how the system actually works

Heathrow publishes two airport-level minimum connection times: 1 hour for a same-terminal transfer and 1 hour 30 minutes for an inter-terminal transfer. Both apply to single-ticket passengers staying airside; both are minimums, not recommendations. A single-ticket booking will not be sold to you with a connection that breaches the applicable airport or airline MCT, so a 70-minute T5-to-T5 itinerary is not coming through any global distribution system. The official guidance is on heathrow.com/connecting-flights.

Airlines often set their own MCT above Heathrow's. The clearest example is British Airways, which raised its T5-to-T5 same-terminal MCT from 60 minutes to 75 minutes on 9 January 2024, to absorb the operational margin lost to congestion and delayed inbounds on its busiest connecting itineraries. BA's T3-to-T5 inter-terminal MCT stayed at 90 minutes because the airside Flight Connections bus and the security re-check on the destination side already build in that margin. Source: BA's own travel-partner notice. Other carriers publish their figures on their own connections pages.

For the wider flight-cluster context, see the Flight information hub.

The most consequential question at any Heathrow connection is whether your flights are on one ticket or two. On a single ticket (whether direct with one airline, an alliance through-ticket, or an interline through-ticket between two airlines that have an agreement), bags are through-checked to the final destination, the boarding pass for the second leg is usually issued at first check-in, and you stay airside throughout the transit. You follow purple signs from the gate to the next terminal or the next gate; the airport's stated MCTs apply.

On separate tickets booked yourself (the classic self-connection where you have stitched two airlines together for a cheaper fare), Heathrow treats you as a full arrival followed by a full departure. You clear UK Border Force, collect any checked bag at baggage reclaim by terminal, exit landside, re-enter the departure terminal, check in for the next flight, drop the bag, and re-clear security. The standard MCT does not apply to you. Realistic floor 3 to 4 hours; longer at peak. The physical mechanics of moving between terminals on this path sit on the full inter-terminal transfer guide, and Heathrow's own walk-through is on the heathrow.com guide to connections. If the second flight leaves from Gatwick rather than Heathrow, treat it as its own journey again: the inter-airport options and timings sit on Gatwick to Heathrow.

Heathrow uses two sign colours to route connecting passengers, and the rule is binary. Purple Flight Connections signs lead the airside path: from the arriving aircraft to the airside Flight Connections bus or to the next gate within the same terminal, staying inside the secure zone throughout. You do not enter the UK on the purple path. You re-clear security at the destination terminal and walk to the onward gate.

Yellow Arrivals signs lead the landside path: down to UK Border Force, through immigration, on to baggage reclaim, and out into the arrivals hall. Once you have followed yellow into the arrivals hall, you cannot return airside without going back through full check-in and security at the departure terminal of the next flight. Through-ticketed passengers follow purple from the gate; separate-ticket passengers follow yellow. The purple route is the one the airport's stated MCTs are built for.

Three scenarios require connecting passengers to clear UK immigration before reaching the next flight, despite the connection happening airport-to-airport on the same day.

The first is the self-connection on separate tickets covered above. The second is anyone who chooses to leave the airport between flights regardless of ticketing; the moment you step landside you re-enter as a fresh departing passenger for the next flight. If you do have the hours to leave, see what is worth doing on a long layover, from Windsor to central London.

The third is the international-to-domestic case, where the international arriving leg connects onto a UK domestic flight (for example, JFK to Heathrow onward to Edinburgh or Manchester). Heathrow routes these passengers through biometrics and UK immigration before security on the domestic side, even on a single ticket, to prevent boarding-pass swaps that would otherwise let an international arrival enter the UK on a domestic flight. UK immigration and passport control covers the eGate eligibility list and the staffed-desk fallback.

On a single ticket with one airline or one alliance, bags are through-checked to the final destination as the default, and you collect them only at the end of the journey. On a single ticket across alliances or with an interline agreement, bags are usually through-checked but the safest move is to confirm at the first check-in desk that the tag reads through to your final airport, not just to Heathrow. On separate tickets, your bag is tagged only to Heathrow on the first leg, you collect it at baggage reclaim by terminal, and you re-check it with the next airline. Through-checked luggage rules covers the wider picture including hand-luggage limits and the rules for liquids picked up airside on a connection.

Heathrow's four operating terminals are physically separate. Terminal 2 connections and Terminal 3 connections share the central terminal area and are linked airside by an underground walkway with travellators, around 10 minutes on foot. Terminal 4 connections sits south of the runway pair on its own access road; reaching it airside means the Flight Connections bus. Terminal 5 connections sits on the western edge with its own station and approach; airside connections to T5 also use the Flight Connections bus, and short-haul British Airways flights often depart from the T5B and T5C satellites reached by a transit train from the main T5 building.

The airside Flight Connections bus runs every 6 to 10 minutes and links all four terminals, signed throughout the airport with the purple Flight Connections markers. Door-to-door times depend on the terminal pair, the inbound gate, and the security re-check queue on the destination side. The inter-terminal transfer page has the per-route bands, the landside rail alternatives that apply on separate-ticket connections, and the BA-specific recommended times.

At the gate on arrival, look up rather than ahead: gate-end staff and the airport's flight-information screens carry the purple Flight Connections signage, and the next gate or transfer point is usually one of the first things signed. The airline's transfer desk is the right second stop if you have lost time on the inbound leg and the connection is now at or below the MCT; the desk re-issues boarding passes for a missed flight and rebooks the onward leg under the airline's own rules.

If you do miss the next flight, the rule splits cleanly. On a single ticket, the airline rebooks you onto the next available service at its expense, and UK261 compensation may apply if the missed connection caused a long delay arriving at the final destination. On separate tickets, the second airline has no obligation; you buy a new ticket at the walk-up fare, claim on travel insurance if you have it, or absorb the cost. Heathrow arrivals and what happens after you land and Heathrow departures and what to do before you fly cover the rest of the sequence on each side of the connection.