If your P800 says you owe tax but you have already paid it through PAYE, you may be wondering how to correct errors on a P800 without making the problem worse. A P800 is HMRC’s calculation of whether you have paid the right amount of income tax for a tax year, but its figures can be wrong when pay, benefits, pension details or allowances have been reported incorrectly. This guide explains what to check, how to contact HMRC, what evidence to gather and what to do if the calculation is not changed.
Why a P800 might be wrong
A P800 is usually produced after HMRC compares information from your employer, pension provider and other sources with the tax code used during the year. It may show a refund, an amount of underpaid tax or a result stating that no further action is needed. The calculation is based on information available to HMRC, so an error in one payroll submission can affect the whole result.
Common problems include an incorrect total pay figure, tax deducted being left out, a pension being treated as employment income, or two employers both giving you the same personal allowance. Benefits in kind, taxable redundancy payments and changes of job can also create confusing results, particularly when payroll records were updated late. Check the tax year shown on the P800 before comparing it with payslips, because a figure from one year cannot normally be corrected by using evidence from a different year.
The most important first step is to identify which figure is wrong and why. Compare the P800 with your final payslip for that tax year, P60s from each employer, P45s issued when you left a job and pension statements where relevant. If the P800 includes a source of income you never received, or omits tax that was deducted, write down the amount, the employer or payer involved and the documents that support your position.
How to correct errors on a P800
If the calculation appears incorrect, contact HMRC using the details on the P800 or the official GOV.UK guidance for income tax. Explain that you are querying the calculation and give the tax year, your National Insurance details if requested, the disputed figures and a clear description of the error. Do not assume that sending a new Self Assessment tax return is the correct solution, because most PAYE-only P800 issues are dealt with directly by HMRC.
Have supporting information ready before you make contact. Useful evidence can include P60s, P45s, payslips, pension payment records, correspondence about taxable benefits and confirmation from an employer that payroll figures were amended. If the error came from an employer, ask the employer to correct its payroll submission as well as contacting HMRC; otherwise HMRC may continue to receive the same incorrect information.
A practical way to communicate is to set out the issue in a short list: the amount shown on the P800, the amount you believe is correct, the difference and the document proving it. Ask HMRC to explain any figure you do not understand and note the date, method of contact and any reference number. The official HMRC calculation should be checked against the source records rather than accepted simply because it appears on a formal notice.
For security, use the contact route shown in genuine HMRC correspondence or locate the service through GOV.UK rather than relying on an unexpected message containing a payment link. HMRC may need to verify your identity before discussing the record. If you are posting documents, keep copies and use a suitable delivery method, but do not send original documents unless HMRC specifically asks for them.
Checking income allowances and tax codes
A P800 error is not always a simple arithmetic mistake. The underlying issue may be that HMRC has treated a payment as taxable, failed to include an allowance or used a tax code that did not reflect your circumstances. Review the income sections carefully, including employment pay, pensions, savings interest where relevant and taxable benefits, then check whether the tax code shown on payslips matches the code HMRC says it used.
Some questions arise because a payment has been confused with employment income. For example, someone asking does maternity allowance need income tax should distinguish Maternity Allowance from statutory maternity pay and from other earnings, because the tax treatment and reporting route can differ. Likewise, a question such as how much tax free childcare can i get concerns a government support scheme rather than a PAYE tax code, so it should not automatically be entered as taxable income when checking a P800.
Allowances can also be misunderstood. If you are asking what does the property allowance cover, you are dealing with rules for certain property income rather than an automatic reduction of employment tax. Rental income, allowable expenses and property-related allowances can require a separate calculation, and a P800 may not be the right document for resolving a property tax dispute. If you have property income, several income sources or overseas income, consider getting help from a qualified tax adviser or accountant before asking HMRC to change figures.
Check whether a tax code was changed during the year, particularly after starting or leaving a job, receiving company benefits, claiming Marriage Allowance or beginning a pension. A code can be correct for one part of the year but still produce a year-end adjustment if payroll information was late or duplicated. Tax code history, rather than the final code alone, can show why the total tax deducted differs from the amount expected.
Worked example and next steps after contacting HMRC
Suppose an illustrative P800 for one tax year says that you underpaid £620. You compare it with your records and find that the P800 includes employment pay of £32,000 from Employer A and £18,000 from Employer B, but the P60 from Employer B shows that £1,100 of tax was deducted and the P800 appears to count only £500. The apparent error is not necessarily the whole £620, but the missing £600 of tax may materially change the result.
You would gather both P60s, relevant payslips and any notice explaining the calculation, then tell HMRC exactly where the figures differ. HMRC may confirm that the employer’s record was incomplete, ask the employer to submit corrected information or explain that another adjustment offsets the difference. This example is illustrative only: the final liability depends on the applicable allowances, tax bands, benefits, pension position and the records HMRC accepts.
After HMRC reviews the matter, ask what will happen next and how you will receive an amended calculation. If a refund is due, check whether it will be paid directly, issued by cheque or dealt with through a later tax code, as the available method can depend on the circumstances. If tax is owed, ask about the payment deadline and whether the amount can instead be collected through a future PAYE code; do not ignore the notice while waiting for a response.
One common mistake is to challenge only the final refund or bill without checking the individual income and tax figures that produced it. Another is to compare the P800 with a current payslip, even though the P800 usually relates to an earlier tax year. Keep a written record of what HMRC says and ask an appropriately qualified and, where relevant, regulated tax adviser: which evidence supports the correction, and does the issue require an amended employer submission or a separate Self Assessment correction?
When a P800 problem needs further help
Many straightforward PAYE discrepancies can be resolved by checking records and contacting HMRC, but more complicated cases deserve additional care. This includes several employments, self-employment, rental income, capital gains, non-UK residence, trusts, high-value benefits or a dispute about whether income belongs to a particular tax year. The P800 may be only one part of the overall position, and correcting it without considering other income could leave the wider tax return wrong.
If you are already required to file a Self Assessment return, the P800 may not be the final word on your liability. Check whether HMRC is asking you to submit or amend a return, and do not report the same income twice. A qualified accountant or tax adviser can help reconcile PAYE records with a tax return, especially where an employer has corrected a payroll report after a return was filed.
If the disagreement continues, ask HMRC to explain its evidence and the review or complaint route available for your situation. A complaint is not the same as a formal appeal against a tax decision, and the correct process depends on the notice and the issue being challenged. Keep copies of letters, calculations and proof of submission, and obtain independent professional advice if a substantial amount, repeated HMRC error or potential penalty is involved.
Do not pay an amount solely because you are worried about missing a deadline without first understanding the notice, but do not assume that contacting HMRC automatically pauses every obligation. Deadlines and payment arrangements can depend on whether the P800 is an informal calculation, a demand linked to another notice or part of a Self Assessment position. Confirm the current procedure with HMRC or a suitable tax professional, because tax rules, administrative processes and contact arrangements can change.
Key Takeaways
To correct a P800, start with the tax year and identify the precise discrepancy rather than disputing the result in general terms. Compare the calculation with P60s, P45s, payslips, pension records and evidence about benefits or other income. Then contact HMRC through an official route, explain the difference clearly and provide copies or details of the supporting evidence requested.
Check whether the apparent error is really connected to a tax code, duplicated employment record, missing tax deduction or the treatment of a separate allowance or payment. Maternity Allowance, Tax-Free Childcare and property income have their own rules and should not be added to a P800 calculation without checking how they are treated. If your affairs involve several income sources, property, overseas matters or Self Assessment, professional advice can prevent one correction from creating another problem.
A P800 is a useful end-of-year check, not a substitute for reviewing your own records. Keep the amended calculation and any HMRC correspondence, verify how a refund or underpayment will be dealt with, and confirm current figures and deadlines on GOV.UK. This independent guidance is not HMRC or regulated tax advice, so obtain case-specific help where the amount is significant or the position remains disputed.