Heathrow to Stansted Airport

I have just looked on the Transport for London - tfl.gov.uk website and they suggest just over 2 hours door to door - Heathrow Express to Paddington, the Elizabeth Line to Liverpool St then the train to Stansted. I would allow longer.

It could take you anything up to 2 hours from landing to exiting Heathrow. If it’s a train strike day, the journey will be difficult and expensive.

If you aren’t booked on a through ticket, I would allow 5+ hours from landing. It’s not a journey I would relish whilst jet lagged on a transport system that’s unfamiliar.

I've not done this myself but Rome2Rio transportation site says 1h20m by National Express Coach. Of course that is going to depend on traffic levels at the time of day you are traveling as well as the day of the week. You'd have to figure in time to wait for the coach and although I did not check the National Express Coach website, the Rome2Rio site says they go 5 times a day so you could possible have a couple of hours wait.

If you have not already bought this ticket combination I would seriously think about whether this is a good idea.

Can you take a flight from LHR to your actual destination? It would be better if this could be accomplished all on one ticket so you are protected if your arrival flight is delayed or cancelled.

Off hand I'd have thought a couple of hours or more.

If the Stansted Express train from Liverpool Street station is up to its usual standard you will want to add even more time - it doesn't have the best record in the world.

If you use the National Express coach you will be on roads completely across the full width of London giving you plenty of opportunities for traffic to put the kibosh on. So leave extra time.

Not really a connection made in heaven. Leave plenty, plenty of time.

I often take the National Express bus from LHR to Stansted. I usually buy a ticket that is flexible as a delayed flight is very possible these days. It should take about 1 hr 15 mins to 1 h 30 mins for direct coaches (depending on the time of day). There are some coaches that have a connection through Victoria, so make sure you don't select those (3 hrs). I hope you don't have a flight scheduled out of Stansted for the same day - that would not be a good idea unless you had about a 6-8 hour layover.

Minimum times between flights

The minimum time you should contemplate making a transfer between Heathrow and Stansted is 5 hours.

Terminal layout at Heathrow is such that if you are flying into or out of Terminals 4 or 5 the bus will take 25-30 minutes longer than using Terminals 2 or 3.

Road congestion warning!

The route of about 65 miles (105km) between Heathrow and Stansted is along heavily congested motorway/freeway. Mondays to Fridays between 6.30am and 10am and 3.30pm and 7pm traffic congestion is routine, expect delays of 15 minutes or more. There can also be severe congestion late Sunday afternoon/ early evening. But at anytime the slightest incident can bring the road to gridlock.

https://www.londontoolkit.com/travel/heathrow_stansted_bus_transfer.htm

"When" you would be doing this is an important factor in 'how long' it could take.

A bus is subject to traffic, but 3 different trains, with luggage, is not something I would find appealing.

I would skip the Heathrow Express and take the Elizabeth Line to Liverpool Street Station and then the Stansted Express to Stansted Airport.