Martin Lewis issued a four day warning to those paying their energy bills by direct debit in England, Scotland and Wales.
The Money Saving Expert took to Twitter to urge direct debit customers to take a meter reading before midnight on Friday June 30.
This is because the new Ofgem Price Cap will be coming in from midnight on Saturday July 1 so energy rates will be dropping.
Ofgem's new price cap is set at £2,074 for the average annual energy bill which is several hundred pounds less than the current Price Guarantee rate of £2,500.
With energy rates set to drop by around 17% on average, you will need to make sure your units are recorded correctly.
If they are not you may end up being charged more than you owe.
For example, if you use electricity on Saturday, but your energy provider thinks you used it on Thursday, you'll be charged at the higher rate.
If you submit a meter reading before the drop at midnight, your energy provider will have the most accurate and up to date information on your usage in order to work out your next energy bill.
In one of his tweets, Martin said: "Submitting a reading within a few days of the change (many let you backdate a few days too) reduces the risk of their 'estimating' going against you (though there's always a chance a discrepancy could end up in your favour)."
The Money Saving Expert coined this week as "Meter Reading Week".
Martin also urged households to take a photo of their meter reading in case they can't submit it to their provider on the same day.
However, he did note that people who have smart meters or are on prepayment meters do not need to submit a meter reading to their energy supplier.
In his tweet he said: "IT'S METER READING WEEK! Prices fall an avg 17% across Eng, Scot & Wal this Sat as the price cap drops (more for higher users who have gas, less for lower elec only users)
"Got working smart/prepay meter? You NEEDN'T do a meter reading Pay by direct debit? Submit a reading.
"With monthly direct debit, firms estimate your usage, and assign it to a certain period, so submitting a reading within a few days of the change (many let you backdate a few days too) reduces the risk of their 'estimating' going against against you (though there's always a chance a discrepancy could end up in your favour).
"Take a pic of the meter for belt 'n' braces. Please share with anyone this is relevant to."
