Just curious to know to what extent travellers chose to fly (or ride Eurostar ) to Europe or Ireland to avoid paying the high rate for APD.
Dublin would of course make much sense as it doesnt attract APD plus, going to US, immigration is cleared there. But need to buy tickets separately
Any thoughts?

Apd?

"Air Passenger Duty (APD) is an excise duty which is charged on the carriage of passengers flying from a United Kingdom or Isle of Man airport on an aircraft that has an authorised take-off weight of more than 5.7 tonnes or more than twenty seats for passengers."

Oh - thanks -- I knew about that just couldn't place the acronym.

How much is ADP and would it even come close to off-setting cost of getting - taking Eurostar implies OP is talking about from London.

ADP is a 78£ tax levied when you leave UK by air for a flight over 2000 miles. It does not exist in Ireland (including NIR ) or Scotland highlands & islands, nor in most countries in continental Europe

edit 78£ in economy cabin, much more in premium cabins

I have actually chosen to fly through Heathrow and pay the tax rather than have a transfer within the US.
I guess you have to weigh up whether the hassle (and cost) of getting to another country to start your journey outweighs the convenience of departing from a UK airport.

I am intrigued by the question.

Why would you care? Is it a separate charge on top of the ticket, or built into the ticket price?

Yes I know -- see up thread. I have never given it a second thought really (except when flying BA on an AA award ticket). I fly/travel through the UK if it makes most sense for my Itinerary, I avoid it when transiting through the UK doesn't make sense. If there is a reasonable way to avoid it like say open jaw in to LHR and home from CDG I might do that instead of the reverse. But really not a huge issue IMO.

Not an issue to me either. Cost is built into the ticket

Generally the only time you see it is when you're using mileage or points for tickets, as the airlines pass through "taxes and fees" as a cash requirement on top of the miles required.

For flights departing the UK and traveling under 2000 miles, the cheapest rate - for passengers in the lowest class of service on the plane - usually economy - is £13. For passengers traveling in any higher class of service it's double - £26. For flights traveling more than 2000 miles, the cheapest rate is £78; for pax in any higher class of service - premium economy, business or first class - it's double that, or £156. Next April the long-haul rates will stay at £78 for economy, but go up to £172 for the other classes. APD is waived on passengers transiting the UK for 24 hours or less; however the incoming and outgoing flights need to be on the same ticket.

(Some airlines, most notoriously British Airways, also add their own "carrier-imposed" fees on award tickets that aren't taxes at all; the technical term for them is "profit." The combination can make the total cost - in miles and dollars/pounds - quite high for "award" tickets.)

Airfare is based on complicated algorithms that the airlines guard with a vengeance, but it's overwhelmingly a supply-and-demand situation. Yes, the APD is built into tickets bought for money, but that doesn't mean that flying through the UK is necessarily the cheapest, nor the most expensive alternative. For example, for next May, a round trip on British Airways from London to Johannesburg in business class is US$2714 most days. On the same days, a round trip from Amsterdam to Joburg on BA, using the very same flights between London and JNB, is $1677, over a thousand dollars less. Would an hour coming from AMS to London and going back be worth a grand? Even if you wanted to fly in business class between London and Amsterdam in order to board the flight that just turns around and takes you back, the cost for that round trip ticket is $301. If you can survive coach for a couple of hours, the cost is half that, $156.

The total price of the ticket is what is important, not how the fare is made up. From Belgium, flying business class intercontinental, it is sometimes cheaper to fly Brussel-LHR-US on British Airways than it is to fly direct from Brussel or Amsterdam.

I agree, why would anyone avoid flying through to avoid a fee if the total price of the tickets was the same or less than other methods? this doesn't make any rational sense

Well, it shows how odd (or insane) pricing is. It does not reflect at all costs incurred by the airline.