At what point in the year would you expect to use more than your DD?

Ildhund

Of course there can be no 'average' that fits for anybody, let alone everybody. It's not unlikely that these figures apply to a 'normal' English household, which has gas central heating and consumes 2700 kWh of electricity a year. The question was quite clear, and I think this chart provides a reasonable answer: you can expect your monthly bill to exceed your DD in October, and see it drop below the DD again in April. Of course, this won't necessarily apply every year, and possibly hardly ever in Lerwick or Torquay. 

Scot_39

The OP specifically mentioned heating in the post as the reason Nov near doubled (40% to 80%).

The question of whether the data includes or does not include heating is therefore very relevant to the OP's question.

When the bill in question includes primary heating - it often - as my example above - makes a huge difference to the range of seasonal variation.

The Ovo chart goes from c7 to c11 % - 4% difference -mines goes from sub 5 to well over 15% in peak heating months - a 12% difference.

And my use vs averaged - to exclude the near doubling of electric SC -  for that as including heating - over the last 3 years - taking a guess at Dec 24 (average of last 2 years) - Oct has not been over the average. 

Nov has 2 out of 3 times - but by nowhere near the levels of Dec / Jan.