Fare discrepency

Hi, Quite a bit I’m afraid.

The Oyster system combines legs of a journey into one journey, which in your case is Chafford Hundred to Watford Junction. Fenchurch Street to Aldgate and Euston Square to Euston are recognised out-of-station interchanges (OSI). The off-peak fares between Euston and Watford Junction only apply if the whole journey is between those two stations, or any intermediate stations on the Lioness line.

Whilst you could break the OSI at Euston by walking from Kings Cross, it probably won’t save you anything because you are curently only paying for zones 1-9 once. If it becomes two separate journeys then you’d be paying twice, albeit that the off-peak leg might be a bit cheaper.

Finally, with contactless you are benefitting from the application of the best combination of caps and extension fares. You’ll find that your journey home is charged at less than the outward journey because the system applies a cap for some zones and adds extension fares for the bits at each end. Oyster can’t do this on the fly, but will apply a credit the next day, but only if the Oyster card is undiscounted.

I would go back to using contactless for your commute, but use the Oyster at weekends when you will benefit from the discounted off-peak fares. Your railcard will obviously give you discounts on journeys further afield from London.