August 19, 2025
By Merranti

HMRC Class 2 National Insurance Error: Why Your Self Assessment Tax Calculation Might Be Wrong

If you’ve received a Self Assessment tax calculation from HMRC that includes Class 2 National Insurance — even though your self-employed income is under the threshold or doesn’t warrant it — you’re not alone. HMRC has confirmed a system error is causing incorrect Class 2 NI amounts to appear on 2024/25 tax return summaries, and they don’t expect to fix it until at least the end of September 2025.

In this blog post, we explain:

What Class 2 National Insurance is
What the HMRC error involves
Who is affected
Whether you need to take action
How to protect yourself from overpaying

If you’re self-employed or submitting a tax return this year, read on to understand how this issue may affect your tax bill.

What Is Class 2 National Insurance?

Class 2 National Insurance (NI) is a flat weekly contribution paid by self-employed individuals whose profits exceed the Small Profits Threshold.

For 2024/25:

Threshold: £6,725
Rate: £3.45 per week
Annual total: £179.40 (if paid for the full year)

Paying Class 2 NI helps build entitlement to certain state benefits, including the State Pension, Maternity Allowance, and Bereavement Support Payment.

If your self-employed profits are below the threshold, you’re not required to pay — but can choose to pay voluntarily to maintain your National Insurance record.

What’s Going Wrong with HMRC’s Calculations?

HMRC is currently issuing tax calculations with incorrect Class 2 National Insurance amounts on them. This is affecting Self Assessment summaries for the 2024/25 tax year.

Known problems include:

Charging Class 2 NI when profits are below the £6,725 threshold
Ignoring voluntary payment elections
Incorrectly doubling Class 2 charges
Omitting the Class 2 NI amount when it should be present

These errors are causing confusion among taxpayers and accountants alike, especially for those who have already submitted their tax return or paid the amount shown.

Has HMRC Confirmed the Error?

Yes. HMRC has publicly acknowledged that:

The Class 2 NI issue is a known system error
They are working on a fix
They aim to resolve it by the end of September 2025
In the meantime, they will continue to issue incorrect calculations

Unfortunately, HMRC has not paused or flagged the affected returns in advance — so incorrect summaries are being sent out as normal.

Who Is Affected?

This issue mostly affects self-employed individuals, particularly those who:

Have profits under £6,725 and shouldn’t be charged
Are making voluntary Class 2 payments (which aren’t showing correctly)
Are filing their Self Assessment tax returns early in the tax year
Rely on HMRC’s online calculation or automated summary to determine what to pay

It may also confuse taxpayers with multiple income sources or those using third-party software.

What Should You Do?

✅ If You’ve Already Submitted Your Tax Return:

Don’t panic – HMRC is aware of the problem
Compare your return to your records – was Class 2 due based on your profits?
Keep a copy of your original submission and HMRC’s summary
If you’ve already paid the amount shown, make a note to revisit your tax account once HMRC has applied the fix later in the year

✅ If You Haven’t Filed Yet:

You can still submit your tax return, but:
Be aware that the Class 2 amount shown may be wrong
If you’re unsure whether to include Class 2, speak to your accountant
You may prefer to wait until after October 2025 when the issue is expected to be resolved

✅ If You’re Below the Threshold:

If your profits are under £6,725 and you didn’t elect to pay Class 2 voluntarily, you shouldn’t be charged
If you did elect to pay voluntarily, but it’s missing or looks incorrect, it may still be recorded properly later

Should You Amend Your Return?

In most cases, no. If the only issue is the incorrect Class 2 NI figure and your actual income and expenses are accurate, there’s no need to amend your return.

HMRC is expected to correct affected calculations automatically after they resolve the system issue.

However, if you’ve:

Overpaid based on the wrong total
Or filed with missing NI contributions you wanted to include

… then you may wish to contact HMRC or speak to your accountant to confirm the best course of action.

Will I Be Refunded If I Overpay?

If you overpay due to the Class 2 error, HMRC should either:

Issue a refund, or
Adjust your account balance once the correction is applied

It’s a good idea to monitor your Self Assessment account from October 2025 onwards to check for updates.

If nothing changes by late October or November, contact HMRC directly to review your case.

Practical Tips to Protect Yourself

✅ Know the threshold: If your profits are under £6,725, you aren’t required to pay Class 2 — but can opt in voluntarily
✅ Use your UTR and tax account to track what you’ve filed and paid
✅ Download copies of all submissions, summaries, and confirmation emails
✅ Set a reminder for October to check your HMRC account for corrections

Final Thoughts

HMRC’s handling of Class 2 National Insurance for the 2024/25 tax year is unfortunately another example of how tax automation doesn’t always get it right. For many self-employed people, the result is confusion — and the risk of overpaying or misreporting.

If you’ve been affected by this issue:

Stay calm
Don’t assume the tax summary is accurate
Seek professional advice if anything on your return doesn’t make sense

At Merranti, we’re already helping clients ensure their Self Assessment tax returns are accurate and that they don’t overpay because of system errors like this. If you’re unsure what to do, our tax team is ready to help.

Get in Touch

Want us to review your tax return or clarify your Class 2 NI status?
Contact Merranti Accounting today — we’ll help ensure your return is filed correctly, and that you only pay what you truly owe.