Ordinarily I wait until the warning comes on the infotainment screen and fill up within a day or two.
I’ve been very good over the last 2 1/2 years and used fuelly. I only missed the first two tank fulls.
My Octy is also a caravan puller (see June/July 2018 for towing figures when I covered more than 4,500 miles).
Today she cracked 40,000 miles and there’s another set of touring figures to add.
Officially my best mpg is 54.5 for a tank full. However, I managed 69.9 for a drive from Cornwall to Teesside.
The amount spent on fuel is inaccurate due to the inability to enter local currency conversions. In Hungary it was 330HUF for a litre – about the same per litre in Sterling.
http://www.fuelly.com/car/skoda/octavia/2017/blueclouduk/689154