The adult TfL price cap for travel within Zone 1 (peak or off-peak) is £6.50. In other words, the maximum amount that will be charged for one day's travel within Zone 1, regardless of the times of travel and the number of journeys made (and, save for one or two exceptions, the modes of travel used), is £6.50. The adult TfL price cap for travel within Zones 1-6 (peak or off-peak) is £11.80. A single fare for an off-peak National Rail only journey from Zone 1 to Zone 6 (e.g. Elstree & Borehamwood) is £3.80. Therefore, a passenger who reaches the £6.50 Zone 1 price cap, and then later in the evening makes a single off-peak journey from St Pancras to Elstree & Borehamwood, should be charged £6.50 + £3.80 = £10.30. However, a single fare for an off-peak London Underground (LU) and National Rail (NR) journey from Zone 1 (e.g. Bank) to Zone 6 is £5.30. And if a passenger, who has reached the Zone 1 price cap, makes such a journey (Bank to St Pancras on LU, then St Pancras to Elstree & Borehamwood on NR), the Oyster system appears to fail to recognise that the journey as far as St Pancras should cost £0, with the journey from St Pancras to Elstree & Borehamwood costing £3.80. Instead, it charges the through fare from Bank to Elstree & Borehamwood, despite the interchange (which involves exiting LU ticket barriers and entering NR ticket barriers) at St Pancras, up to the amount of the Zones 1-6 price cap. Since £6.50 + £5.30 = £11.80 (the very amount of the Zones 1-6 price cap), the passenger is charged £5.30 for the journey from Bank to Elstree & Borehamwood. They should only have been charged £3.80, so they were overcharged by £1.50. Has anyone experienced this problem? Does this problem not occur with the, apparently more accurate, contactless debit/credit card system?