Charlotte Reeves
Why a rejected return causes more hassle than it first appears
Most self assessment returns go through without a murmur. But when HMRC's system spots something that doesn't add up, the return is bounced back — and a rejection is more than a technical blip. You may believe you've filed on time, only to find the clock is still running, with a £100 late filing penalty waiting if a corrected version doesn't land. There's also the admin of amending, rechecking figures and reassuring yourself that nothing else has gone wrong. The good news is that the overwhelming majority of rejections come down to a handful of avoidable problems.
Simple mistakes that catch people out
These small slips account for a surprising share of rejected returns.
- Wrong reference numbers. A mistyped Unique Taxpayer Reference or National Insurance number, or a digit transposed between the two, stops the return matching your HMRC record.
- Incorrect accounting period dates. Dates that don't line up with your year end, or a period HMRC isn't expecting, trigger an automatic query.
- Name and address mismatches. A trading name, a former address or a middle name HMRC doesn't hold can be enough to fail validation.
- Ticking boxes carelessly. Selecting the wrong self-employment or partnership page, or indicating you're not resident when you are, sends the return down the wrong route.
- An unsigned or undeclared return. The declaration is a legal statement, and forgetting it means the return isn't complete.
Missing or mismatched information
HMRC now receives a great deal of third-party data — bank interest, dividends, pension contributions, employment income from P60s, Gift Aid claims. If your return disagrees with what's already on record, expect a letter.
- Omitted supplementary pages for rental income, capital gains, partnership income or foreign income, even where the amounts are modest.
- Employment income that doesn't match your P60, often caused by copying a figure from an earlier payslip or overlooking a second job.
- Interest and dividends entered incorrectly — for example, using the amount received rather than the gross figure HMRC expects.
- Missing Gift Aid donations, student loan repayments or pension contributions that affect your tax band.
- Blank boxes where HMRC expects a zero, particularly on supplementary pages.
Calculation errors, especially around expenses
This is where rejections overlap with HMRC enquiries. The most frequent culprits are:
- Claiming disallowable expenses — client entertaining, fines, personal clothing, or drawings run through the business account.
- Mixing the cash basis and traditional accounting part way through a return, or claiming capital allowances on something already covered by the annual investment allowance.
- Home and motoring costs claimed in full when a business-use proportion is needed, or mileage rates applied on top of actual running costs.
- Partnership profit splits that don't match the partnership return, and losses claimed in the wrong year.
- Rounding and decimal point slips, where pence become pounds and turnover is overstated tenfold.
Keep your workings. If HMRC queries a figure, a simple schedule showing how you arrived at it resolves most questions quickly.
Technical and submission problems
Sometimes the arithmetic is fine and the submission itself fails. Returns filed before all the figures are final, software that hasn't been updated, an interrupted connection mid-submission, or two attempts creating a duplicate return can all cause confusion. Paper returns bring their own risks — lost post, the wrong year's form, or arriving after the deadline even though you posted in good time. Filing early, with final figures, avoids most of this.
How to check your return before you send it
A short review routine pays for itself many times over.
- Reconcile everything to your accounts, bank statements and records before you start keying in.
- Read the return as a whole once it's complete, checking each figure against its source.
- Compare to last year — an unexplained swing in turnover or expenses is exactly what invites a query.
- Check the period dates, your UTR and NI number character by character. It's dull, but it's where errors hide.
- File with time to spare. If HMRC rejects the return, you need room to correct and resubmit before 31 January.
If a return is rejected, don't panic. Read the error message, fix the specific problem and send it again — most rejections are resolved in a single attempt. And if you spot a mistake after filing, you generally have twelve months from the filing deadline to amend it, so it's far better to correct it yourself than wait for HMRC to ask.
