On What Grounds Can HMRC Reject Your Self-Assessment Tax Returns
- MAZ
- 3 days ago
- 18 min read
Reject vs. enquiry: what HMRC actually does
First, it helps to understand what “rejection” really means in HMRC-speak.
HMRC can:
● Reject or not accept a return – usually because of a technical or fundamental problem. This often happens at the point of filing (especially online) if the return fails validation checks or misses key information.
● Open an enquiry or compliance check – where the return has been accepted but HMRC wants to verify the figures, ask for evidence, or correct errors.
This article focuses on the grounds for rejection or non-acceptance, but I’ll flag where something is more likely to trigger an enquiry instead of an outright rejection. The distinction matters, because:
● A rejected return may mean HMRC treats you as not having filed at all. That can lead to late filing penalties and interest if it isn’t sorted quickly.
● An accepted return under enquiry counts as filed, even if HMRC later amends it.
Missing the legal filing deadline
Let’s start with the obvious one – but also one people underestimate.
The legal filing deadlines for Self Assessment are:
● Paper returns: normally 31 October following the end of the tax year(so paper returns for 2023/24 were due by 31 October 2024).
● Online returns: normally 31 January following the end of the tax year(so online returns for 2023/24 are due by 31 January 2025).
If you try to send a paper tax return after the 31 October deadline without a reasonable excuse, HMRC is not obliged to treat it as valid. In practice, they may still process it, but you’ll be treated as having filed late and may face penalties.
For online returns:
● HMRC’s online system won’t usually “reject” on timing alone – it will accept late returns.
● However, from a legal standpoint, a return filed after the deadline is late, and HMRC can charge late filing penalties even if the system has accepted the submission.
So, strictly speaking, late filing is more of a penalty issue than a “rejection” ground. But I include it because many people confuse “system accepted it” with “HMRC is happy”. They’re not the same thing.
Actionable tip:Even if you miss the deadline, file as soon as possible. Penalties and interest escalate over time, but filing stops the clock on certain charges.
Using the wrong form or tax year
It sounds trivial, but it does happen: people submit the wrong version of the tax return.
Common problems include:
● Sending a paper SA100 for the wrong tax year (for example, filing a 2022/23 version for the 2023/24 year).
● Using outdated or unofficial forms that don’t align with HMRC’s current layout or questions.
● Filing a paper return when HMRC has specifically required online filing (for example, certain complex cases or those using specific software).
HMRC can treat such returns as not validly made, because the law requires returns to be made “in the form” HMRC specifies for that year.
If that happens, HMRC may:
● Return the form and ask you to resubmit on the correct version; and
● Potentially treat you as having not filed at all until a valid return is received.
What to do instead:
● Always download the current year’s forms from GOV.UK, not from a random website.
● Check the tax year printed on the form – it should match the year you’re filing for (e.g. 6 April 2023 to 5 April 2024).
Missing mandatory information or signatures (for paper returns)
For paper returns in particular, HMRC can reject your tax return if essential parts are incomplete.
Typical reasons include:
● No signature on a paper SA100 (or the wrong person signed – for example, someone who doesn’t have authority).
● Missing National Insurance number or Unique Taxpayer Reference (UTR) where they are required and can reasonably be provided.
● Leaving out mandatory boxes that HMRC needs in order to process the return at all (for example, no figures on income pages when you’ve indicated that you have that type of income).
With online filing, the system usually doesn’t let you submit unless the required fields are completed. With paper filing, however, human error can easily creep in.
In practice, HMRC might:
● Return the incomplete return to you, asking for missing information; or
● Log it but still treat it as not validly filed if the omission is serious enough.
The key risk is that you think you’ve filed, but HMRC says you haven’t, and penalties start to build.
Practical checklist for paper filers:
● Have you signed and dated the SA100?
● Is your UTR present and correct?
● Are your personal details complete (name, address, NI number)?
● Have you included all relevant supplementary pages (e.g. self-employment, property) and filled them in?
Online validation failures: HMRC software won’t accept your return
If you’re filing online (either through HMRC’s portal or commercial software), you may run into validation errors that stop the submission going through.
This is one of the most common ways your tax return is effectively “rejected” before it even reaches HMRC.
Common validation issues include:
● Inconsistent figures – for instance, the total income on the main return doesn’t match the sum of all the detailed pages.
● Incorrect formats – dates, postcodes, or other fields entered in a way the system doesn’t accept.
● Invalid UTR or NI number – if these don’t match HMRC’s records, or are typed incorrectly, the submission may fail.
● Tax computation errors – if the software calculates tax in a way that doesn’t align with HMRC’s rules for that year.
Most software will give you an error message such as “Return failed HMRC validation” with an error code. HMRC hasn’t accepted your return yet – so as far as they’re concerned, you haven’t filed.
How to fix it:
● Read the error message carefully and correct the relevant entries.
● Make sure you’re using the correct tax year in your software.
● Double-check personal details against official documents.
● If you’re stuck, your software provider or an accountant can often decode the HMRC error message.
Trying to file when you’re not actually in Self Assessment
HMRC can also push back if you try to file a Self Assessment return when they don’t think you should be in the Self Assessment system.
For example:
● You send in a paper SA100 without having been issued with a notice to file (SA316), and without having registered properly.
● You used to be in Self Assessment but HMRC has since removed you, and you try to send a new return without a current notice.
Legally, you can still submit a tax return voluntarily in some circumstances, but HMRC’s systems don’t always handle that smoothly. They may return the form or simply not process it as a formal Self Assessment return.
This doesn’t usually lead to penalties, but it can lead to confusion about:
● Whether HMRC accepts your figures.
● Whether overpaid tax will be repaid or offset.
If in doubt, it’s best to:
● Register for Self Assessment properly if you meet the criteria (e.g. self-employed income over the threshold, significant untaxed income, rental income, etc.).
● Or, if you simply need to claim a refund and don’t meet Self Assessment criteria, use a tax refund claim form instead (for example, form P800 or R40, depending on the situation).
Filing for the wrong tax year or wrong dates
Sometimes people muddle up tax years. UK tax years run from 6 April to 5 April, which can feel counter-intuitive.
Common mistakes:
● Including income from the wrong tax year – for example, putting employment income from May 2024 on a 2023/24 return instead of 2024/25.
● Using calendar year figures instead of tax year figures.
● Filing for the wrong year entirely in the online system (for example, lodging a 2022/23 return when you meant 2023/24).
The online system won’t always “reject” the return outright, but HMRC can later treat it as:
● Not a valid return for the year you think you’ve filed for; and/or
● Something that still leaves you with an outstanding obligation for the correct year.
In some cases, especially where the tax year clearly doesn’t match the income period, HMRC may come back quickly and ask you to correct and resubmit.
Practical tip:Before you start, confirm the tax year you’re dealing with:
● 2023/24 tax year: 6 April 2023 – 5 April 2024
● 2024/25 tax year: 6 April 2024 – 5 April 2025
Make sure all your figures (payslips, P60, P45, bank interest, rental income) match that period.
Serious errors, obvious impossibilities or nonsense entries
HMRC’s systems are designed to flag entries that plainly don’t make sense. While some of these result in enquiries, others can cause the system to reject or bounce the return.
Examples include:
● Huge negative numbers where they cannot exist (for instance, negative salary).
● Claiming reliefs that are incompatible with your circumstances (e.g. certain niche reliefs with no corresponding income).
● Totals that simply don’t add up – such as tax deducted larger than the income itself.
In milder cases, HMRC will accept the return and later open an enquiry. In more extreme cases, particularly where the figures can’t be processed, HMRC can treat the return as invalid and ask you to submit a corrected version.
My best advice here:
● Be realistic and consistent. If you’re claiming a very large loss or refund, that’s fine – but make sure it’s properly backed up and arithmetically sound.
● If you’re unsure how to show something unusual, look at HMRC’s guidance on GOV.UK or speak to a professional.
Incorrect or mismatched personal details
HMRC cross-checks your details across systems. If basic identity information doesn’t match, your return can hit a wall.
You might run into problems if:
● Your name, address, or date of birth don’t match HMRC’s records.
● Your UTR or NI number is incorrect or belongs to someone else.
● You’ve recently changed name or address and HMRC’s records haven’t been updated.
Often, this won’t lead to a formal “rejection” but to a delay or a request for clarification.
However, in some cases (especially online), the submission may not be accepted in the first place.
Action point:If you move house or change your name, tell HMRC and update your details through your Personal Tax Account on GOV.UK or by contacting them directly.
Not including required supplementary pages
Self Assessment is modular. The main SA100 is only part of the picture. Depending on your situation, you may need extra pages, such as:
● SA103 (self-employment)
● SA105 (UK property)
● SA106 (foreign income)
● SA108 (capital gains)
HMRC can refuse to accept a return as complete if you:
● Declare that you have, say, rental income or capital gains, but don’t include the relevant supplementary pages, or
● Include pages that are mostly blank or incomplete while still claiming you have that type of income.
Online, the system normally prompts you to add the relevant sections. With paper, it’s easier to miss.
Strictly speaking, HMRC may accept the SA100 but later consider it incomplete, and in some cases they might treat it as not a valid return if key pages are missing.
Practical approach:
● Before you start, list all your income sources for that year: employment, self-employment, dividends, interest, rental, foreign income, gains, etc.
● Check on GOV.UK which supplementary pages you need for each type of income.
● For online filing, make sure you tick the correct boxes so the software includes those sections.
Attempts to amend a return outside the allowed window
Once you’ve filed a tax return, you can usually amend it within 12 months of the normal filing deadline.
Example:For a 2023/24 return:
● Filing deadline (online): 31 January 2025
● Amendment deadline: 31 January 2026
If you try to submit an amendment after that date through the normal Self Assessment route:
● HMRC may reject the amendment (i.e. not treat it as a valid amendment).
● Instead, they might ask you to make an “overpayment relief” claim or take a different route.
This isn’t quite the same as rejecting an original return, but it’s still HMRC saying “no” to what you’ve sent. The original return stands unless and until changed through the proper channels.
What to do if you’re out of time:
● Read HMRC’s guidance on “overpayment relief” on GOV.UK.
● Be aware there are time limits (usually 4 years from the end of the tax year concerned) and specific conditions.
When HMRC thinks a return is fraudulent or deliberately misleading
In more serious situations, HMRC may decide not to treat a return as valid if they believe it is:
● Deliberately false or fraudulent, or
● Not a genuine attempt to meet your legal obligations.
This tends to arise in:
● Cases involving fake repayment claims (for example, refund scams).
● Returns submitted in someone else’s name without proper authority.
● Situations where figures are clearly fabricated to obtain tax advantages.
In those cases, HMRC may:
● Reject the return.
● Refuse to process repayments.
● Open a civil or criminal investigation.
For the average honest taxpayer who simply makes mistakes, this isn’t something to lose sleep over. But it’s a reminder that your return is a legal declaration and HMRC takes deliberate falsification very seriously.
Grounds for “correction” vs. outright rejection
It’s also important to understand that HMRC has the power to correct a tax return without rejecting it altogether.
Under legislation, HMRC can amend your return to:
● Fix obvious arithmetical errors.
● Correct obvious omissions.
● Adjust the return where the tax calculation doesn’t align with the entries.
They’ll normally send you a revised calculation if they do this. You have the right to challenge or amend it if you disagree.
So not every “problem” with a return is a ground for rejection. Many mistakes are simply corrected or queried. Rejection usually happens when:
● The return is not in the right form.
● Mandatory information is missing.
● The system can’t process what you’ve sent.
● There’s a fundamental mismatch or invalidity.
Practical checklist to keep HMRC happy
Here’s a quick, practical checklist to reduce the odds of HMRC rejecting or bouncing your return:
● Check the tax year: Make sure you’re using the right year’s form or online version.
● Confirm your details: UTR, NI number, name and address must match HMRC’s records.
● Use the right pages: Add self-employment, property, CGT, foreign income pages as needed.
● Sign and date paper returns: And make sure the correct person signs.
● Check your maths: Ensure totals and subtotals add up.
● Match the period: Use figures for the correct tax year (6 April to 5 April).
● Submit on time: Remember 31 October (paper) and 31 January (online).
● Respond to HMRC letters: If they query or return a form, act quickly.
Relevant thresholds and rules (as at recent years)
While the exact figures can change, it helps to anchor things with some current context (always double-check on GOV.UK for the latest year you’re dealing with):
● Personal Allowance (2023/24 and frozen for now):
● £12,570
● £12,570 – tax-free income for most people, though it tapers if your income exceeds
● £100,000
● £100,000.
● Basic rate tax: 20% on income between
● £12,571
● £12,571 and
● £50,270
● £50,270 (excluding Scottish income tax on non-savings/non-dividend income, which has its own bands).
● Higher rate: 40% on income between
● £50,271
● £50,271 and
● 125,140
● 125,140.
● Additional rate: 45% on income over
● £125,140
● £125,140.
Self Assessment is typically required if, for example:
● You’re self-employed and earned more than
● £1,000
● £1,000 from self-employment.
● You received more than
● £2,500
● £2,500 in untaxed income (e.g. rent, commissions).
● Your total income is over
● £100,000
● £100,000.
● You have capital gains above the annual exempt amount, or other specific circumstances.
If you should be in Self Assessment but aren’t, HMRC can issue a notice to file and expect a return. Failing to file a valid return after that notice is one of the firmest grounds HMRC has for penalties and enforcement.
How Google’s “People-First Content” ideas actually help you here
You mentioned Google’s 2025 Core Updates and the focus on “People-First Content”. Interestingly, the principles that make a good, trustworthy article are very similar to the principles that make HMRC comfortable with your tax affairs:
● Experience – You’re describing your situation accurately and honestly, based on real records (payslips, bank statements, invoices), not guessing.
● Expertise – You take the time to understand HMRC’s rules or get help when needed, so the return reflects the rules correctly.
● Authority – You rely on credible sources like GOV.UK guidance and professional advice rather than hearsay from forums or social media.
● Trustworthiness – Your return is consistent, transparent and you can back up the numbers with documentation if HMRC asks.
Thinking with a “people-first” mindset means:
● You’re not trying to game the system, either with search engines or with tax returns.
● You focus on clarity, honesty and completeness.
● You’re willing to fix errors promptly if they’re pointed out.
If you approach your Self Assessment in that spirit, you dramatically reduce the risk of HMRC rejecting it or putting you under unnecessary scrutiny.
What to do if HMRC does reject or bounce your return
If you receive a letter or an online message saying HMRC hasn’t accepted your return, don’t panic. Work through these steps:
Read the wording carefully
Are they saying the return is invalid, incomplete, or simply that there’s an error to correct?
Identify the specific issue
Is it a missing signature, wrong tax year, missing pages, or an online validation failure?
Correct and resubmit promptly
Treat it as urgent, especially if deadlines are close or have passed. The quicker you fix it, the better your position on penalties and interest.
Keep evidence of submission
Keep copies of paperwork, online submission receipts, and any HMRC correspondence. This can help if there’s a dispute later over whether you filed on time.
Appeal penalties if appropriate
If the rejection or confusion leads to a late filing penalty but you genuinely had a reasonable excuse and acted promptly, you may be able to ask HMRC to cancel or reduce the penalty.
Seek professional help for complex cases
If you’re going in circles with HMRC, having someone who deals with Self Assessment daily can save time, stress and sometimes money.
A final word of encouragement
Dealing with HMRC and Self Assessment can feel intimidating, especially when you’re worried about your return being rejected. But most problems are fixable and many are preventable once you understand how HMRC thinks and what the system checks for.
If you:
● Use the correct year and forms,
● Provide complete and honest information,
● Keep an eye on key deadlines, and
● Correct any issues promptly,
then HMRC is very unlikely to reject your tax return outright.
And if you ever find yourself stuck between error codes, missing signatures and confusing letters, it’s absolutely fine to ask for help. A short conversation with someone who understands the system often untangles what feels like a massive knot.
FAQs
Q1: Can someone’s Self Assessment be rejected just because their PAYE tax code was wrong during the year?
A1: Well, it’s worth noting that HMRC won’t reject a Self Assessment purely because your PAYE tax code was wrong. What they care about is whether your return reflects what actually happened. So if your code under‑ or over‑deducted tax, you simply report your true income and the tax deducted from your P60s or P45s, and the return will correct the position. Where problems arise is if the figures on your return don’t line up with what HMRC already holds from your employer. In practice, that mismatch doesn’t usually lead to outright rejection, but it can trigger checks or a correction. The key for you is to copy the numbers exactly from your PAYE documents and, if the tax code was clearly wrong, add a brief note in the “additional information” box so HMRC understands why things don’t look neat on their side.
Q2: Can HMRC reject a return if someone has multiple jobs and the income totals don’t match their own records?
A2: In my experience with clients who juggle two or three jobs, the main issue isn’t rejection, it’s inconsistency. HMRC receives pay and tax details from each employer, and your Self Assessment should mirror those figures. If your total wages on the return don’t match the sum of all P60s and P45s, HMRC’s system will usually accept the return but flag the discrepancy later. It would be very unusual for them to throw the whole return out just for that, but they may correct the figures or open an enquiry. A simple way to avoid this is to line up each job in a small spreadsheet and check that the total pay and tax you enter are exactly what the documents show, even if one employer has made a mistake that needs dealing with separately.
Q3: Can a taxpayer’s return be rejected because they used a salary tax calculator instead of actual payslips?
A3: This is a common pitfall. Using a UK salary tax calculator is fine for planning, but HMRC expects your Self Assessment to be based on real evidence, not estimates. If your figures are clearly “rounded guesses” and don’t match HMRC’s PAYE data, they’re unlikely to reject the return at the gate, but they may amend it or challenge the entries. Consider a nurse in Manchester who loses a couple of payslips and plugs their salary into an online calculator – the result might be close but still off enough to cause trouble. The safer route is to get replacement documents from the employer or retrieve data from your Personal Tax Account, then file. If you absolutely have to estimate, note this clearly and correct the return as soon as accurate figures are available.
Q4: Can HMRC reject a Self Assessment if someone underreports gig economy income from platforms like Uber or Deliveroo?
A4: Technically, HMRC won’t reject the return on submission just because you’ve underreported gig income; the system doesn’t always know that at the point of filing. However, HMRC increasingly receives data from gig platforms, and if your return doesn’t align with those figures, that’s when issues begin. Rather than rejection, you’re more likely to face a compliance check or amendments, and if they consider the omission deliberate, penalties can be steep. I’ve seen drivers in London assume that small amounts paid into PayPal “don’t count” and then be surprised when HMRC already has platform data. If you use gig apps, download your yearly statements, declare the full income, then claim allowable expenses honestly to keep yourself on solid ground.
Q5: Can a Scottish taxpayer have their return rejected because they used rest‑of‑UK tax bands by mistake?
A5: It’s an easy mix‑up, especially for people who move between Scotland and England during a tax year. HMRC won’t normally reject your Self Assessment outright for applying the wrong bands; instead, their system recalculates the tax using the correct set of rates for the income they classify as Scottish. That said, if your return claims reliefs or credits that don’t fit your residency status, you could see HMRC correct the return or query it. The best approach is to check where HMRC treats you as resident for income tax band purposes, which is based on your main address on their records, and let the Self Assessment calculation apply the right rates automatically rather than forcing numbers that match an online calculator using different assumptions.
Q6: Can someone’s Self Assessment be rejected if they work remotely from abroad for a UK employer?
A6: For remote workers, HMRC is more interested in residence and source of income than blanket rejection. A return won’t usually be rejected just because you were overseas; the risk comes if you try to claim “non‑resident” status without completing the correct residence and overseas pages, or you ignore foreign tax issues entirely. I’ve worked with IT contractors in Portugal who report only UK PAYE and leave out a double tax position completely. In those scenarios, HMRC can treat the return as incomplete and ask you to resubmit with the right supplementary pages. If you’re living abroad while working for a UK employer, it’s wise to use the residence section properly and, where needed, seek advice on double taxation rather than hoping HMRC ignores the cross‑border angle.
Q7: Can HMRC reject a Self Assessment because pension contributions are entered incorrectly?
A7: It’s surprisingly common for people to muddle up gross and net pension figures, especially with personal pension schemes. If the numbers don’t stack up with what HMRC expects from providers, they typically won’t reject the whole return, but they may recalculate the relief or ask you for evidence. A rejection is more likely if your entries break the calculation rules, for example claiming impossible amounts of relief with no income to support them. Think of someone on a modest salary entering a very large annual allowance figure as if it were a normal contribution – HMRC’s software might not accept that. The safest practice is to copy figures from your pension statements exactly and remember that workplace pensions under auto‑enrolment and personal pensions can be treated differently for relief purposes.
Q8: Can a landlord’s Self Assessment be rejected if they forget to include mortgage interest or claim it incorrectly?
A8: For landlords, the usual issue is not rejection but miscalculation. HMRC won’t kick your return back simply because you missed some allowable finance costs or claimed them in the wrong box. More likely, you either pay too much tax (by not claiming what you could) or invite questions if your figures look unusual compared with your rental income. For example, a property owner in Bristol who declares £20,000 rent and no expenses at all might not be rejected, but HMRC may wonder if something’s missing. Mortgage interest rules have changed over the years, with restrictions on relief, so if you’re unsure, it’s better to under‑claim and adjust later than to over‑claim in a way that stops the return from calculating properly.
Q9: Can a self‑employed person’s return be rejected if they mix business and personal expenses?
A9: Mixing business and personal costs is one of the most common self‑employment issues I see, but it rarely leads to outright rejection. HMRC usually accepts the return, then challenges whether the expenses are allowable if they open an enquiry. Where rejection can occur is if the way you’ve entered expenses breaks the structure of the form, such as putting negative numbers where they shouldn’t be, or submitting totals that lead to impossible results. Imagine a freelance designer in Leeds who enters a “minus” figure in turnover to offset personal costs – the system may simply refuse the return because the numbers no longer make sense. The clean way is to record all income, then claim business‑only costs, and use adjustment notes if there’s any unusual treatment you need to explain.
About the Author
Maz Zaheer, AFA, MAAT, MBA, is the CEO and Chief Accountant of MTA and Total Tax Accountants, two premier UK tax advisory firms. With over 15 years of expertise in UK taxation, Maz provides authoritative guidance to individuals, SMEs, and corporations on complex tax issues. As a Tax Accountant and an accomplished tax writer, he is renowned for breaking down intricate tax concepts into clear, accessible content. His insights equip UK taxpayers with the knowledge and confidence to manage their financial obligations effectively.
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