Starting taking state pension with backdating

[Bill67]

My tax question is about starting to take the new state pension and exercising the option to backdate it for 52 weeks (i.e. take in arrears). I want to know whether the one-off payment of this arrears sum is taxable when it is received (in the current tax year) or taxed (somehow) as if it were received in the previous tax year when the entitlement first existed.

For example, imagine someone (who is already more than a year beyond state pension age) retiring from full time work on Apr 5th and then commencing taking state pension on Apr 6th. The 52 week of arrears would obviously be received sometime early in the first year of retirement and only add to that tax year’s pension income, in which case all pension income would be within basic tax rate and not affected by final year of employment.

Is that the correct interpretation though?
I’ve researched this online and got a thoroughly confusing mix of responses, hence posting here.

[D&C]

When you receive the State Pension payment isn't relevant for tax purposes, it's what you were entitled to that counts.

So in your example the 52 weeks of backdated State Pension would be taxed as income of 2025/26, not 2026/27. The fact DWP only pay you those 52 weeks worth in say May 2026 doesn't matter from a tax perspective.

If you backdated it from say 6 July 2026 then only 39 weeks would fall into the 2025/26 tax year.

There is HMRC information about the basis on which State Pension is taxed here.

https://www.gov.uk/hmrc-internal-manuals/employment-income-manual/eim75700#taxable-amount

[Bill67]

Thank you. I couldn't see anything specific in EIM 75700 relating to the particular circumstance I described. However, is this generic statement what you were referring to: "Subject to the following 2 exemptions, the taxable amount is the amount of pension accruing in the tax year. This may be different from the amount actually paid in a tax year." ?

So if a one-off payment of 52 weeks in arrears is made when commencing state pension, what is the practical mechanism for deducting tax, given teh payment may be made before or after the self-assessment return for the previous year (when the entitlement began) has been submitted? Is the current year (when the one-off arrears sum is paid) tax code used and then the ultimately correct answer arrived at when this return is submitted, resulting in an adjustment payment to/from the taxpayer?

[D&C]

That does cover your scenario exactly, you have decided to put the pension into payment from 6 April 2025 i.e. backdated the claim by 12 months.

So the first 52 weeks are all taxable in 2025/26, the fact that DWP can only put the money in your bank account during 2026/27 is irrelevant.

LITRG also explain this here,

https://www.litrg.org.uk/pensions/state-pension/tax-state-pension#5

If you have already filed the tax return for the tax year the entitlement relates to (2025/26) then you would have to amend your Self Assessment return for that year. Which is not a complicated process.

If you don't do that reasonably quickly don't be surprised if HMRC decide to open a formal investigation into your return.