Flying into Heathrow, planning train travel to Cardiff

What time is you arrival from the US?

Asking because how much time you will spend going through immigration at Heathrow is often dependent on how many flights land at the same time AND how well immigration is staffed.

Heathrow is huge.

My route is overnight from LAX or SFO to LHR. Over the years the shortest amount of time was 20-30 minutes to 2 hours. My flights arrived between 1 and 2pm. Terminal 5.

At a minimum give yourself 1.5-2 hours. Better be early than late. Lots of food outlets and shopping options at Heathrow. The walk to the Heathrow Express will be a minimum of 20 minutes.

Don't buy two separate tickets for your trip to Cardiff. Buy a single ticket from Heathrow to Cardiff, and let the search engine suggest the best way, which might be via Paddington or via Reading.

Re last post. This is bad advise.
I have given up using the RailAir to Reading as more expensive and probably slower and using Heathrow Express route costly too
Off Peak on the Underground to Paddington with a Contactless Card is £3.50.
Advance Single from Paddington to Cardiff appear to start from £25.00
The problem is what leeway are you doing to build into your itinerary

I'd disagree with rogerbrown in this instance about squeezing every last pence out. The Heathrow Express a little in advance is £5.50 to Paddington and not time specific. I don't think I'd Piccadilly Line to Earl's Court or South Kensington (when it returns to service) and change tubes to Paddington. Too much faffing about for the price of a cheap espresso. If you really must pinch pennies at least use the TfL Rail. Then as rogerbrown said about the Advance to Cardiff...

Thanks for everyone's comments. We arrive at 10:30 am. From your comments, I think we should plan for 1 1/5 - 2 hours minimum to get to Paddington. My thinking is that we're going to be jet lagged so finding our way for the first time from Heathrow to Cardiff (and to our Airbnb) will be a challenge enough. Spending a few extra dollars on the faster route from Paddington to Cardiff will be worth it for us. We'll look at departure times, then, from Paddington starting sometime after 1:30 which leaves us time for a leisurely, unrushed path from our plane to our Airbnb. Your comments have really helped--I'm thinking this might be a good new section for the Man in Seat 61. As far as I can tell, he doesn't address this question on his wonderful site? Or perhaps I've just missed it.

Go to www.gwr.com & put in for a journey from Heathrow Rail to Cardiff for about 1 month ahead from now at roughly the time of day you expect to travel. Make a note of the prices & times.

Now go to www.TrainTickets.com and do the same but before you click search - click Advanced options and tick the box that says AVOID LONDON. This will now show you can get from Heathrow to Cardiff for roughly half the price of the first option above by going the short distance to Hayes & Harlington and then onto another stopping train to Reading and then joining a Great Western Inter City Express to Cardiff.

The time taken to reach Cardiff for both the above is around 2 hours 30 minutes from Heathrow. Note that the second option splits the tickets into sections and thus reduces the fare. It also avoids the expensive Heathrow Express into Paddington. It is not train specific between Heathrow & Reading but is from Reading to Cardiff. (I have caught the ‘wrong’ GWR express and not had a penalty fare - depends on the staff & how busy the train is). Also note that the cheaper advance specific train tickets usually get loaded around 10 weeks ahead but this can vary. Play around with dates now and see what happens to the fares.

Thank you! This is incredibly helpful. It's so great to have this forum for advice.