When you give your opening readings, the first thing that must happen is they are sent for validation. This is a standard industry process to check that your readings are (roughly) inline with what the energy industry expects. Once these checks have been done, your readings are sent to your previous supplier.

The whole process normally takes 2-6 weeks from when you send your readings, to when your previous supplier gets them.

Gas and electricity readings are validated separately by different companies, so it’s normal for your previous supplier to get these at different times.

The validation process

Validation is done by independent companies. Whilst they are appointed by your new supplier, importantly they are independent of both your old and new supplier, to make sure their decisions are fair. They check if your opening reading is sensible by estimating your opening reading themselves (based on what the energy industry knows about your meter) and comparing the reading you've given against their estimate. If it's similar then your reading will pass validation. If your opening reading fails validation, the independent validation company will tell both suppliers to use their estimated reading instead.

An estimated reading is calculated from your last known reading and counting on by how much energy they expect your meter to have used since then.

Last Reading + Estimated Usage = Estimate Opening Reading

The added Estimated Usage is calculated specific to your meter using your meter's estimated annual usage, which is calculated and managed in a centralised industry database using historic usage data. See our help page How are my charges calculated? for more information about your estimated usage.

When the validation company compares your reading against their own estimate, they check if your reading is within certain bounds around their own estimate.

  • The lower bound is the last meter reading taken. Your meter should never run backwards, so your opening reading should never be lower than a previous reading.
  • The upper bound is calculated as the reading if you used 2.5x the Estimated Usage expected.


A customer gave a reading to their energy company on 1st October 2016 of 32,536. They switch to So Energy, and their supply start date is 1st December.

The validation company expects that from 1st October and 1st December this meter will use 333 kWh. This means that the upper bound would be 32,536 + 2.5 x 333 = 33,369 lower bound = 32,536. When we receive an opening reading, if it is between 32,536 and 33,369 it will be validated. If it's outside of these then it will fail and we'll use the estimate of 32,536 + 333 = 32,869.

Once the validation process has been completed the opening reading that is being used is sent over to your previous supplier so they can use it to produce your final bill with them.

I have provided an opening reading, why didn't you use it?

If the reading you have given is outside the reading 'bounds' it will fail validation and won't be used. That's not to say it isn't correct. The usual reason for this is that your previous supplier may not have had a recent reading from you.

If you would like to use your reading rather than an estimate, it is possible to dispute the estimated reading used for you. Any final bill which may have already been generated will need to be changed if a new reading is agreed (See My opening reading is wrong for more details).

If the opening reading provided is too high

Following on from the example above, if we received an opening reading of 34,000 it would fail validation because its greater than the upper bound (33,369). A reading of 32,869 would then be used to open their account.

If the opening reading is too low

If we received an opening reading of 32,300 it would also fail validation because it's lower than the previous reading (lower bound 32,536). A reading of 32,869 would then be used to open the account.

I gave my readings after the opening reading window

If we haven’t received an opening reading from you by 5 days after the date your supply starts the validation company will automatically generate an estimated reading for you. Unfortunately, even if you give us readings on the 6th day, the estimated reading may have already been sent off to your previous supplier to close your account with them.

That's not to say that we can't use your reading, just that there is a chance that you will receive a final bill based on an estimate instead and we will need to open your account using this same estimate. If this has happened and you want to start your account on your own reading we may be able to 'dispute' the estimate (See - My opening reading is wrong for more information). If the reading is changed, it will change your final bill from your previous supplier too.

I didn't provide an opening reading

If we haven’t received an opening reading from you, we'll use the estimated opening reading to start your account with us and send the opening estimate over to your previous supplier so they can close your account with them at the same point.

If you have recently given your previous supplier a reading, then the estimated reading should be fairly accurate, so you shouldn't worry too much. It is still worth double checking that the opening estimate is roughly in line what your meter is showing. If this reading isn’t quite right, we'll need to get this changed. If this is the case, please get in touch with us so we can look into this.