Capping TfL, how to verify/determine ahead of time?

[dasfvzcx]

I sometimes travel with the following pattern:

- Take a (GWR) train from Reading to Paddington before 6:30
- Change to Elizabeth at Paddington and go to Farringdon/Moorgate [I used to change card, because that was cheaper, but that is not the case anymore]
- Travel back, from Farringdon to Paddington
- Take a GWR train from Paddington to Reading *after* 19:00. If I checked in before 19:00 at Farringdon, I'll use different card (which is most of the time)

Now, my question is, in situations where I used the same card for all this travel (and it was all off-peak, but in the morning peak cap is counted towards) it would say I reached the Zone 1(-2) cap.
From a dumb calculation, the Elizabeth <-> Farringdon/Moorgate journeys, don't add to the cap, and from what I understand the Reading <-> Paddington fares should have some it apportioned to Zone 1-2 travel.

Can anybody explain what's going on here, and whether there are sources out there that I've missed?

 

[JonathanH]

I understand the Reading <-> Paddington fares should have some it apportioned to Zone 1-2 travel.

It doesn't necessarily work like that. The unpublished extension fares are sometimes set in such a way that the 'inner' caps don't apply. Essentially they manipulate the extension fares to try and ensure that the Reading cap applies.

The extension fares can only be determined by making journeys around the system as there is no published source.

Do you have examples of what you have actually been charged?