Transport for London is trying hard to get everybody to use their Contactless credit and debit cards, rather than using Oyster - which is more expensive for them to run.
To push Contactless TfL are making frequent announcements over the Public Address in stations that "Contactless is the same price as Oyster". They even make the same claim on their website. Both are lies.
There are two main scenarios where Contactless fares are NOT the same price as Oyster.
1. Weekly usage for any period which doesn't start on a Monday.
If you are starting on a Monday, then the Monday-Sunday cap will mean that you pay the same as a standard 7 day travelcard. However, if you start on any other day, you will pay more - possibly a lot more.
So, if you are starting your travel on anything other than a Monday - it is cheaper to buy a travelcard on your Oystercard.
2. If you are going to be using Transport for London services for a month.
Despite the (false) claim that Contactless costs the same as Oyster, TfL do actually admit that regular users should buy a monthly travelcard - but they bury it in their website, and make no mention on their Public Address announcements.
I hate to think how much regular commuters are wasting on weekly Contactless fares, when they should be buying a monthly travelcard.
It is shameful that TfL lie about Contactless - and thereby steal from their customers.