National Insurance Refund Claims Move Online At HMRC

HMRC has started writing to people whose employer may have deducted too much Class 1 National Insurance in error, telling them they could be due a refund.

Since April 2026, recipients have been able to claim online through a new digital service set out in GOV.UK guidance, rather than only returning the paper form attached to the letter.

• The online claims service has been available since April 2026; GOV.UK’s guidance was published 31 March 2026 and updated 22 June 2026, and the service only works if you enter the claim reference number printed on your letter
• It covers overpaid Class 1 National Insurance only; employers and personal representatives cannot use it
• The standard time limit for a National Insurance refund claim is four years from the end of the relevant tax year, currently reaching back to 2022 to 2023
• 35 qualifying years are needed for the full new State Pension, and at least 10 for any State Pension at all
• Why HMRC is sending these National Insurance refund letters

Not every National Insurance overpayment triggers a letter. HMRC writes only when its systems suggest an employer deducted too much Class 1 National Insurance in error.

This letter type is logged as Letter CA4361 on HMRC’s own checklist of genuine contacts.

Each one carries a claim reference number, entered into the new online service alongside bank details to apply. Without that reference number, the online route cannot be used, and HMRC directs claimants to check how to claim a National Insurance refund a different way instead.

Employers and personal representatives cannot use the digital service, and a personal representative handling a deceased person’s estate must follow the separate instructions in their own letter.

The letters do more than confirm the Class 1 point. They also set out HMRC’s records of any Class 2 and Class 3 contributions paid, plus any National Insurance credits received.

The recipient is asked to check these are accurate, since an error here is unlikely to surface on its own.

If a letter does not mention Class 2, Class 3 or National Insurance credits, HMRC’s records show none were paid or received.

This matters well beyond the immediate refund, because qualifying years underpin the State Pension: 35 are needed for the full new State Pension, and a minimum of 10 for any State Pension at all.

National Insurance still isn’t reconciled the way Income Tax is

The letters are a rare example of HMRC proactively flagging an overpayment, and that is what makes them newsworthy: they highlight a gap in the rest of the system.

Unlike Income Tax, National Insurance does not automatically reconcile at the end of the tax year.

Each employer calculates and deducts Class 1 contributions in isolation, with no visibility of what an employee earns, or pays, elsewhere, so cross-employment overpayments are not something any single employer can identify or correct.

HMRC does not routinely check an individual’s whole National Insurance record, so outside the specific cases covered by these letters, spotting an overpayment and claiming it back typically falls to the individual.

Overpayments arise for several recurring reasons:

• Having more than one job, where each employer deducts National Insurance independently and can together breach the annual maximum across the Primary Threshold to Upper Earnings Limit band (£12,570 to £50,270 a year in 2026 to 2027, taxed at 8% then 2%)
• A payroll error, such as an employer using the wrong National Insurance category letter
• Continuing to work past State Pension age, when employees should stop paying Class 1 National Insurance altogether (their employer still pays theirs)
• Being employed and self-employed at once, where Class 1, Class 2 and Class 4 contributions together can exceed the annual maximum
• Paying voluntary Class 3 contributions unnecessarily, often because the 35 qualifying years for a full State Pension were already held

What this means for you

If you’ve received one of these letters, you can now apply for your refund without waiting for the postal form to make its way back to HMRC.

How to claim if you’ve had a letter

1. Check the letter for a claim reference number — the online service cannot be used without one.
2. Read the Class 2, Class 3 and National Insurance credits details in the letter, since these come from HMRC’s records and are worth checking against your own.
3. Apply using the GOV.UK service linked above, or the paper form attached to your letter if you’d rather not apply online.
4. Use the “check when you can expect a reply from HMRC” tool on GOV.UK for an idea of current processing times, then wait for HMRC to confirm the outcome in writing.

If you haven’t had a letter but think you’ve overpaid NI

These letters only cover a narrow category of Class 1 cases, so most people who have overpaid National Insurance won’t receive one and need to claim proactively themselves.

The route depends on which class is involved.

A Class 1 overpayment without a letter is usually claimed by writing to HMRC’s National Insurance Contributions Office with your National Insurance number, the tax years involved, and evidence such as P60s, P45s or payslips.

A Class 4 overpayment uses form CA5610, and a Class 2 overpayment uses form CA8480, available online or by post.

The normal deadline is four years from the end of the tax year in which the overpayment happened, though longer limits can apply in some cases, such as an official HMRC error.

It’s worth contacting HMRC even about an older overpayment rather than assuming you’re out of time. Tax Rebate Services’ guide to claiming a National Insurance refund sets out the evidence and process for each route in more detail.

Preventing the overpayment in the first place

If you know you’ll have more than one job through the tax year, applying for National Insurance deferment before the year starts can avoid the overpayment altogether, instead of waiting months for a refund afterwards.

The relevant form is CA72A, and HMRC needs to receive applications for the 2026 to 2027 tax year by 14 February 2027. It’s one of the more overlooked options for people with multiple jobs, agency work or umbrella company arrangements.

Does a national insurance refund affect your State Pension?

A Class 1 refund arising from having more than one job does not normally reduce your qualifying years.

You’ll typically still have paid National Insurance above the Lower Earnings Limit in at least one of your jobs.

A Class 2 refund is different: if you had no other contributions in that tax year, it could turn a qualifying year into a gap.

Either way, it’s worth checking your National Insurance record on GOV.UK or in the HMRC app after any refund is processed, to see how it’s affected your record.

Is the national insurance letter genuine?

An unexpected letter from HMRC can understandably prompt some anxiety about scams.

Genuine National Insurance refund letters arrive by post and carry a claim reference number. The letter type — Letter CA4361 — has appeared by name on GOV.UK’s own checklist of genuine HMRC contacts since June 2024, so you can cross-check it there.

HMRC does not send refund links by text message or email, so anyone contacted that way should treat it as suspicious.

If you’re unsure, GOV.UK’s guide to checking whether an HMRC letter is genuine is a safer way to confirm it.

So is signing into your Personal Tax Account or the HMRC app independently, rather than using contact details from the letter itself. Claiming is free — through the online service or the paper form — so there’s no need to pay a third-party claims firm to do it for you.

Key Takeaways

• Most National Insurance overpayments don’t trigger a letter, so it’s worth checking your own position even if you haven’t heard from HMRC
• Letters also list Class 2, Class 3 and National Insurance credits — check these against your own records, since they can affect your State Pension
• Genuine letters come by post with a reference number — HMRC never asks for a refund via a text or email link, and you never need to pay a claims firm.