HMRC to review 107,000 tax calculations after error

What the beneficial ordering rule is and why HMRC systems get it wrong

What the beneficial ordering rule is and why HMRC systems get it wrong

The beneficial ordering rule is a tax principle that determines the order in which different types of income are taxed against the personal allowance. HMRC's computer systems have applied this rule incorrectly since at least 2021, causing tax-free allowances to be allocated in the wrong sequence across employment, pension, savings and dividend income.

Under the Income Tax Act 2007, the personal allowance, which is £12,570 for the 2026-27 tax year, must be set against income in the order that is most beneficial to the taxpayer. This means that income taxed at higher rates, such as employment or pension income, should be covered by the allowance before savings interest or dividend income, which generally attract lower rates. The rule is designed to minimise the total tax a person owes across all sources of income.

However, HMRC's computer systems have not consistently followed this order. According to HMRC, the fault was first acknowledged in 2021 and has not been fixed since. The systems have instead applied the allowance in a different sequence, often allocating it to savings or dividend income first, leaving less of the allowance to cover employment or pension income. This can result in more tax being deducted from the main income source than is legally due.

The error affects the calculation of tax codes and the final tax calculations issued on forms such as P800 or through Self Assessment. Because the rule is complex and depends on the exact mix of income, the misallocation is not always obvious to the taxpayer. HMRC has stated that it is now manually reviewing 107,000 calculations from the 2025-26 tax year to correct the problem, but the underlying system fault remains unresolved.

The manual review process is resource-intensive and has led to delays in issuing accurate tax calculations. HMRC expects the volume of manual checks to fall to around 20,000 next year, but this does not mean the fault is fixed. The continued reliance on manual intervention highlights the difficulty of correcting a systemic error that has persisted for several years.

Who is most likely to be affected, with worked examples of mixed income

Who is most likely to be affected, with worked examples of mixed income

People with more than one source of income are most exposed to the error, particularly those who receive employment or pension income alongside savings interest or dividends. The misallocation of the personal allowance can lead to overpayment of tax on the main income source, leaving individuals with a higher tax bill than they should have.

According to HMRC, the fault affects individuals whose income includes both non-savings income, such as wages or a pension, and savings or dividend income. The more complex the income mix, the greater the chance that the beneficial ordering rule is applied incorrectly. For example, a person with a salary of £15,000 and savings interest of £2,000 would normally have the full personal allowance set against the salary, leaving the savings interest to be taxed at the starting rate for savings. If the system instead allocates part of the allowance to the savings interest, the salary is taxed at the basic rate, resulting in an overpayment.

Consider a worked example based on the 2026-27 personal allowance of £12,570. A taxpayer has employment income of £14,000 and savings interest of £1,000. Under the beneficial ordering rule, the personal allowance should cover the first £12,570 of employment income, leaving £1,430 of employment income taxed at 20%, and the savings interest taxed at 0% because it falls within the starting rate for savings. If HMRC's system incorrectly allocates £1,000 of the allowance to the savings interest, then £13,570 of employment income becomes taxable, leading to an overpayment of £200.

Another example involves pension income and dividends. A pensioner receives a state pension of £11,500 and dividend income of £2,000. The personal allowance should be set against the pension income first, leaving £1,070 of pension income taxable at 20%, and the dividends taxed at 0% within the dividend allowance. If the system allocates £2,000 of the allowance to the dividends, then £13,500 of pension income becomes taxable, resulting in an overpayment of £400.

HMRC has not published a full list of affected cases, but the manual review of 107,000 calculations indicates the scale. Those with multiple income sources are advised to check their tax calculations carefully, as the error may not be immediately apparent from the tax code alone.

How to check your own P800 or Self Assessment calculation line by line

How to check your own P800 or Self Assessment calculation line by line

Checking a P800 or Self Assessment calculation requires comparing the income amounts and the personal allowance allocation against the beneficial ordering rule. Taxpayers should verify that the personal allowance has been applied to employment or pension income before savings or dividend income, and that the correct tax rates have been used.

For a P800, which is issued by HMRC after the end of the tax year, the calculation shows total income from all sources, the personal allowance, and the tax due. The first step is to confirm that the income figures are accurate, including any employment, pension, savings interest, and dividend income. According to HMRC, the P800 should reflect the correct amounts reported by employers, pension providers, and banks.

Next, check the allocation of the personal allowance. The allowance should be set against non-savings income first, such as wages or pension, up to the full amount of £12,570 for 2026-27. Only if non-savings income is less than the allowance should any remaining allowance be applied to savings interest or dividends. If the calculation shows that savings or dividend income has used part of the allowance while employment or pension income remains taxable, this may indicate the beneficial ordering error.

For Self Assessment, the calculation is more detailed. The tax return includes sections for employment, pensions, savings, and dividends, and the calculation summary shows how the personal allowance has been applied. Taxpayers should review the 'Tax calculation summary' page, which lists the income types and the allowance used. The same principle applies: the allowance should be allocated in the order that minimises tax, which is generally non-savings income first.

If any discrepancy is found, the taxpayer should contact HMRC or use the online services to request a recalculation. HMRC has acknowledged that the manual review is ongoing, but individuals can proactively check their own figures. Keeping records of all income sources and tax statements is essential for this process.

How to challenge and reclaim an overpayment, and the time limits that apply

How to challenge and reclaim an overpayment, and the time limits that apply

Taxpayers who believe they have overpaid due to the beneficial ordering error can challenge their tax calculation and reclaim the excess. The process involves contacting HMRC with evidence of the correct allocation, and there are specific time limits for making a claim.

According to HMRC, overpayments can be reclaimed by writing to HMRC or using the online form for tax overpayments. The taxpayer must provide details of their income sources and explain why the calculation is incorrect, referencing the beneficial ordering rule. HMRC will then review the case and issue a revised calculation or a refund if the overpayment is confirmed.

The time limit for claiming a refund of overpaid tax is generally four years from the end of the tax year in which the overpayment occurred. For the 2025-26 tax year, this means the claim must be made by 5 April 2030. However, HMRC has stated that it is proactively reviewing 107,000 calculations from that year, so some taxpayers may not need to make a claim themselves. Those who are not part of the manual review but suspect an error should still file a claim within the time limit.

For Self Assessment, the process is similar. Taxpayers can amend their tax return within 12 months of the filing deadline, but for overpayment claims, the four-year limit applies. If the error is discovered later, it may still be possible to claim under the 'discovery' provisions, but this is more complex and may require professional advice.

HMRC has not specified a separate process for the beneficial ordering fault, so standard overpayment procedures apply. Taxpayers should keep copies of all correspondence and evidence, including P60s, P45s, and bank statements showing interest, to support their claim.

What changes next year and why HMRC expects the volume to fall

What changes next year and why HMRC expects the volume to fall

HMRC expects the number of manual checks for the beneficial ordering error to fall to around 20,000 in the next tax year, but the underlying system fault remains unfixed. The reduction is attributed to changes in the income mix of taxpayers and improved identification of affected cases, not to a correction of the computer system.

According to HMRC, the manual review volume for the 2025-26 tax year is 107,000, but for the following year, the number is projected to drop to approximately 20,000. This reduction is not due to a fix in the software, as the fault acknowledged in 2021 has not been resolved. Instead, HMRC has stated that the lower figure reflects a change in the composition of taxpayers' income, with fewer individuals having the specific mix of employment or pension income plus savings or dividends that triggers the error.

Another factor is that HMRC has improved its processes for identifying which cases require manual intervention. By using more targeted criteria, the department can focus its resources on the most complex cases, reducing the overall number of manual checks. However, this does not eliminate the risk of error for those who are still affected.

For the 2026-27 tax year, the personal allowance remains at £12,570, which means the threshold for triggering the error is unchanged. The reduction in volume is therefore not due to a change in tax rates or allowances. HMRC has not announced any plans to fix the underlying system fault, so taxpayers with mixed income sources may still face incorrect calculations in future years.

HMRC advises taxpayers to continue checking their tax calculations each year, especially if they have more than one income source. The manual review process will continue, but the lower volume suggests that fewer people will be affected, although those who are will still need to be vigilant.

Frequently asked questions

What is the beneficial ordering fault in HMRC tax calculations?

The beneficial ordering fault affects how HMRC allocates tax-free allowances across different income types, such as employment, pension, savings and dividend income. When a person has more than one income source, the system can apply allowances in the wrong order. This may result in tax being calculated incorrectly, often leaving the individual with an overpayment that they are not liable for.

Which taxpayers are affected by the HMRC calculation error?

The error affects taxpayers who have more than one source of income in the 2025-26 tax year. This includes individuals with income from employment, pensions, savings and dividends. HMRC has identified 107,000 tax calculations that require manual review. Taxpayers with a single income source are not affected, as the fault only arises when allowances are allocated across multiple income streams.

How will HMRC notify taxpayers whose calculations are under review?

HMRC will contact taxpayers whose calculations are affected by the error. The manual review process is being carried out to correct the misallocation of tax-free allowances. Individuals should wait for official communication from HMRC before taking any action. HMRC has not specified a timeline for completing the reviews or issuing revised calculations to affected taxpayers.

Can a taxpayer receive a refund if their calculation is corrected?

Yes, a taxpayer may receive a refund if the manual review finds that they overpaid tax due to the beneficial ordering fault. The correction would adjust the allocation of tax-free allowances, potentially reducing the tax owed. HMRC will issue a revised calculation and any resulting refund automatically. Taxpayers do not need to apply separately, but they should check correspondence from HMRC.

When was the beneficial ordering fault first acknowledged by HMRC?

HMRC first acknowledged the beneficial ordering fault in 2021. Despite this, the error continued to affect tax calculations for the 2025-26 tax year, leading to the current review of 107,000 cases. The fault relates to the order in which tax-free allowances are applied across different income types. HMRC is now manually reviewing the affected calculations to correct any overpayments.