alex_t wrote:
In October I will need to go to Heathrow (zone 6) from Stratford (zone
3). I have Oyster with:
1. monthly travel card for zones 1-3
2. 10£ for pay-as-you-go needs

How will I be charged? For zones 4-6, or 3-6, or 1-6? (I will also
cross zones 1 and 2).
And on return journey, when I will enter in zone 6, and exit in zone 3
(Heathrow - Stratford) - will it be the same?

Assuming those are the only "out of zone" journeys you make on those
days, you should just be charged £1.00 (before 0700 and after 1900
Monday to Friday, all day at weekends) or £1.80 (between 0700 and 1900
Monday to Friday) for a Single for Zones 4-6.

HTH,

Barry