We are arriving into London/Heathrow on a Monday night and plan on taking the Tube to Kings Cross (hotel). We will be in London from Tuesday through the following Monday, staying mostly in zones 1 and 2. I am trying to decide if we need to buy the Travelcard or if we should simply use the Oyster card pay as you go option. The 7-day travel card is 34.10 but that is the same as the PAYG 7-day cap. For either option, when we travel outside zones 1 and 2 (Kew Gardens, Hampton Court), we will pay using money from the Oyster card. We have a London Pass so I don't need the Travel card 2for1 deal; and the travelcard requires a photo (so we would need to have these taken). With the PAYG option,we won't pay more than 34.10 anyway... so why get a travel card? I am wondering how the PAYG is capped... do we just travel on faith that once we reach 34.10 (within zones 1-2), we won't be charged any more? And if there are days that we decide to walk more than use the tube, then we are better off with the PAYG option anyway. Is this correct? Thank you for any help you can give me!
You can load a travelcard to an Oyster card at the Oyster card machine. These work the same, but don't require a photo nor are they eligible for 2 for 1 discounts.
However, my suggestion is to just use PAYG, you'd have to do a lot of tube travel to really make the travelcard pay off. Whereas with PAYG you can monitor your balance and add funds as you need, drawing it down as you hit the end of the trip. I also like to use the numerous coins I accumulate to top off the Oyster as long as there isn't a line at the Oyster card top up machine.
PAYG is only capped weekly if you use contactless payment (either card or Apple/Google/Samsung Pay) and not if you use an Oyster Card which only caps daily (at £6.80 for Z1-2 etc, less for bus only). It works on a Monday-Sunday cycle but that wouldn't be too bad for you. The capping can be broken if you have an incomplete journey (ie fail to tap in or out) but should be fine if you at assiduous on this. It is clever enough to work out that you have made an occasional journey outside of the zones during the week and take that out of the capping.
If you don't have a contactless payment card or device, or you find yours doesn't work, you can still by a 7-day travel card on an Oyster Card. This does not require a photocard. Buy at Heathrow and load on some PAYG for your initial journey + others. There is a slight bonus in that the travel card covers any TfL bus irrespective of zone. If you aren't expecting to do a lot of travel then PAYG alone might be better.
As Marco says, unless you have a contactless credit or debit card (and most US banks do not issue these right now), you will want an Oyster loaded with a 7 Day Travel Card, since there is only daily capping on PAYG Oyster, but not weekly.
"I am wondering how the PAYG is capped"
The capping is automatic - once you reach the daily limit, you aren't charged for any more rides that day. But again, there is no weekly capping with an Oyster, so you would pay £6.80 per day, or, from Tuesday through Sunday (your full days in London) £40.80. So, a weekly Oyster is already cheaper than daily caps for even just those days.
If you are traveling to or from Heathrow on a day when you have an active 7 Day Travel Card for zones 1 and 2, it costs an extra £1.50 (at least off peak when I did it). If your only trip on your arrival day is from Heathrow to your hotel, you'd probably want to do that on PAYG, then load a 7 Day Travel Card the next day.
Thank you for your informative and very helpful replies! Each of you has helped me in making my decision. I now understand how the capping works and more clearly understand the various ways to pay (I have been looking at the Apple Pay system)... I will look at our daily journeys and make a decision. Thank you so much for your time and your informative responses! Best wishes to each of you!