Households are rushing to give energy meter readings today before bills go up from tomorrow (October 1).
Energy bills will be capped at £2,500 a year for a typical household from this weekend - up from an average of £1,971 a year now.
The government's Energy Price Guarantee will come into force from October 1 for two years - replacing the Ofgem price cap.
Before energy bills go up, many homes will be submitting up-to-date meter readings to their energy firms.
The idea is that they can prove how much energy they used at a lower price right up to the point bills go up.
That means they can only be charged for the energy they use, with no quibbling about overcharging.
The last time energy bills went up majorly was April 1.
But the day before, March 31, Brits flocked to give meter readings in droves.
This led to energy firm websites crashing under the strain - including British Gas, Eon, Scottish Power and SSE.
As a result, energy companies have extended their deadlines this time around.
Customers have longer to submit their meter readings - so long as they were taken on October 1.
These are the deadlines for all major energy firms:
British Gas - October 14
Octopus Energy - October 8
Bulb - October 3
E.on - October 6
EDF - October 7
Scottish Power - October 5
Shell - October 31
Ovo and SSE have been approached for comment.
MoneySavingExpert founder Martin Lewis is calling October's meter reading period "meter reading week".
Speaking to Good Morning Britain hosts Susanna Reid and Ben Shephard earlier this week, Lewis said: "Do it today, do it tomorrow, do it the next day. Most firms let you submit the readings up to a week and in some cases two weeks after the date.
“You don’t need to do a reading if you’re on a smart meter that works, on a prepayment meter or you’re on a very cheap fix where the price won't be changing.
“Everybody else should be doing a meter reading. Get it done in the next few days and submit it in the next two weeks.”
Earlier this week energy suppliers were warned they are not doing enough to support customers struggling to pay their bills.
Energy regulator Ofgem found that all but one of the UK's energy suppliers need to make improvements and meet their obligations when it comes to helping customers with financial difficulties.
Energy giants were found to have "severe weaknesses" when it comes to how they support customers struggling to pay their bills.
British Gas was the only company found to have no significant issues in the Ofgem report this week.
TruEnergy, Utilita and Scottish Power were found to demonstrate "severe" weaknesses, according to the regulator.
