Will HMRC check the untaxed interest that I have given them?

RG2015

On 7 December 2025 HMRC issued my P800 for 2024/25 with an untaxed interest amount of £666. This figure was incorrect and I phoned them the next day.

We compared their actual figures with mine and discovered that they didn't have anything from RBS, Naitonwide and First Direct. The revised interest was £1,195 and their agent recalculated my P800 and we agreed my correct rebate. A new P800 appeared online the next day and I claimed my rebate. This appeared in my bank account on 12 December.

HMRC had already issued a revised tax code for 2025/26 on 4 December using the £666 in the calculation. I had expected this to be revised but as yet it has not.

I wondered if HMRC would be checking my figures or perhaps they are not bothered as the effect on my tax is relatively small.

I do find it odd that HMRC have a process for reporting untaxed interest and when it fails they are happy to rely on the clients figures.

Isthisforreal99

The 25/26 figure in your tax code is only provisional until the actual figures are reported at the end of the tax year. Your tax code should probably have been updated but if the interest is indeed higher then you may well owe tax.

friolento

If you update your expected income from interest in your online Personal Tax Acckunt, a new tax code will be issued. To date, HMRC have always accepted the figures I submitted. I don’t know whether they compare my figures with those reported by the savings providers, and I have no visibility of the reported figures

RG2015

friolento said:

If you update your expected income from interest in your online Personal Tax Acckunt, a new tax code will be issued. To date, HMRC have always accepted the figures I submitted. I don’t know whether they compare my figures with those reported by the savings providers, and I have no visibility of the reported figures

Are you saying HMRC have always accepted your interest amounts when they have got your P800 wrong?

RG2015

Isthisforreal99 said:

The 25/26 figure in your tax code is only provisional until the actual figures are reported at the end of the tax year. Your tax code should probably have been updated but if the interest is indeed higher then you may well owe tax.

My tax code for 25/26 was updated on 4 December. However they updated the interest figure I had given them in January 2025 with their completely wrong figure for 24/25. The initial amount I gave them in January was far closer to my expected 25/26 figure.

Albermarle

friolento said:

If you update your expected income from interest in your online Personal Tax Acckunt, a new tax code will be issued. To date, HMRC have always accepted the figures I submitted. I don’t know whether they compare my figures with those reported by the savings providers, and I have no visibility of the reported figures

Do you know how long this takes? I updated my expected interest for 25/26 about a month ago, but no new tax code yet.

Fatferds12

Albermarle said:

friolento said:

If you update your expected income from interest in your online Personal Tax Acckunt, a new tax code will be issued. To date, HMRC have always accepted the figures I submitted. I don’t know whether they compare my figures with those reported by the savings providers, and I have no visibility of the reported figures

Do you know how long this takes? I updated my expected interest for 25/26 about a month ago, but no new tax code yet.

I updated my expected interest amount on 1 December via chat and my tax code was updated almost immediately.  I received notification of the update the next day.  It might be worth contacting them to check. 

RG2015

Albermarle said:

friolento said:

If you update your expected income from interest in your online Personal Tax Acckunt, a new tax code will be issued. To date, HMRC have always accepted the figures I submitted. I don’t know whether they compare my figures with those reported by the savings providers, and I have no visibility of the reported figures

Do you know how long this takes? I updated my expected interest for 25/26 about a month ago, but no new tax code yet.

I had considered doing this for 25/26 but with falling interest rates I did not want to give too high a figure.

I did update my 25/26 figure online in January 2025 to a figure that is quite close to my current estimate. This was incorporated in my initial 25/26 tax code. However HMRC updated this on 4 December with their incorrect 24/25 "actual".

It seems that it is a waste of time updating your estimates, as HRMC will just overwrite them in accordance with their deeply floored system.

RG2015

Fatferds12 said:

Albermarle said:

friolento said:

If you update your expected income from interest in your online Personal Tax Acckunt, a new tax code will be issued. To date, HMRC have always accepted the figures I submitted. I don’t know whether they compare my figures with those reported by the savings providers, and I have no visibility of the reported figures

Do you know how long this takes? I updated my expected interest for 25/26 about a month ago, but no new tax code yet.

I updated my expected interest amount on 1 December via chat and my tax code was updated almost immediately.  I received notification of the update the next day.  It might be worth contacting them to check. 

This is very interesting. I have never used HMRC chat, favouring the online process. I cannot remember how long it took but I am sure it was more than one day.

nottsphil

friolento said:

If you update your expected income from interest in your online Personal Tax Acckunt, a 

There's no need to be calling them that, Frio 😃

Albermarle

Fatferds12 said:

Albermarle said:

friolento said:

If you update your expected income from interest in your online Personal Tax Acckunt, a new tax code will be issued. To date, HMRC have always accepted the figures I submitted. I don’t know whether they compare my figures with those reported by the savings providers, and I have no visibility of the reported figures

Do you know how long this takes? I updated my expected interest for 25/26 about a month ago, but no new tax code yet.

I updated my expected interest amount on 1 December via chat and my tax code was updated almost immediately.  I received notification of the update the next day.  It might be worth contacting them to check. 

I have just checked my personal tax account. 
It says the changed info I entered is still being processed and can take up to 15 days . I made the change on the 8th December.
So hopefully will be enacted early in January.