The figure shown in the Previous Design for MMB isn't always accurate. It's OK for standard bookings, but as soon as you start mixing airlines and UuA and POUGs and what-not it may or may not show the right information. There is a logic to TPs and it's reasonably easy to memorise, I feel, see the BAEC Sticky for how that works. I am sure a lot of people in this forum can just add them up in their head as they go along. But the formal way is to find the Booking Class (or Selling Class) - which is in the More Flight Details line of MMB - and then use the online calculator in BA.com sector by sector.
https://www.britishairways.com/trave...t/public/en_gb
For codeshares, you need to use the airline flight that your bought, rather than the operator.