Self Assessment penalties can arise when a tax return is filed late, tax is paid late or information submitted to HMRC is inaccurate. The initial late-filing charge may be £100, but the total can increase through daily penalties, tax-related charges, late-payment penalties and interest if the return and payment remain outstanding.
Filing and payment are separate obligations. A taxpayer can receive a late-filing penalty even where no tax is due, while someone who files on time but pays late can face interest and late-payment charges.
The safest response to a missed deadline is to file the outstanding return as soon as possible, establish the amount payable and contact HMRC where immediate payment is not possible. Ignoring correspondence generally allows the position to become more expensive and difficult to resolve.
When Self Assessment penalties begin
Online Self Assessment returns are normally due by midnight on 31 January following the end of the tax year. Paper returns generally have an earlier deadline of 31 October.
For example, an online return covering the tax year ending 5 April 2026 is normally due by 31 January 2027. The balancing payment for that year and any first payment on account for the following year are generally due on the same date.
A return filed after the applicable deadline can trigger an automatic £100 late-filing penalty. This penalty normally applies even where the return ultimately shows no tax payable or HMRC owes the taxpayer a repayment.
HMRC’s current Self Assessment penalty guidance explains the filing and payment charges that can arise.
The initial £100 late-filing penalty
The first late-filing penalty is £100. It normally becomes due as soon as the filing deadline has passed without HMRC receiving the return.
The charge is based on the failure to file rather than the amount of tax owed. A taxpayer cannot therefore avoid the penalty by arguing that the return showed a small liability or no liability at all.
The penalty can also apply where tax was paid on time but the return itself was late. Paying an estimated amount does not satisfy the separate filing obligation.
Where HMRC issued the notice to file late, a different filing deadline may apply. The taxpayer should check the date of the notice and any deadline stated by HMRC before assuming that the ordinary 31 January date controls the position.
Daily penalties after three months
If the return remains outstanding for more than three months, HMRC can charge daily penalties of £10 per day.
Daily penalties can continue for up to 90 days, producing a maximum additional charge of £900. This is added to the original £100 penalty.
A return that remains outstanding long enough to incur all 90 daily charges can therefore generate £1,000 of filing penalties before the six-month charge is considered.
Submitting the return stops further daily penalties from accruing. Waiting until the taxpayer has enough money to pay the tax is generally counterproductive because filing and payment are separate matters.
Self Assessment penalties after six months
When a return is six months late, HMRC can charge a further penalty equal to 5 per cent of the tax due or £300, whichever is greater.
This charge is added to the original £100 penalty and any daily penalties already imposed. It can therefore apply even where the outstanding tax is relatively low.
The tax-related figure may initially be calculated using information available to HMRC and revised once the return is filed and the actual liability becomes known.
A taxpayer who has reached the six-month point should still file immediately. Delaying further risks another substantial charge when the return becomes 12 months late.
Penalties when a return is 12 months late
A further penalty normally arises when the return is 12 months late. This is usually 5 per cent of the tax due or £300, whichever is greater.
More severe tax-related penalties can apply where HMRC concludes that information was deliberately withheld. The percentage can depend on whether the behaviour involved deliberate concealment and whether the taxpayer later made an unprompted or prompted disclosure.
These higher penalties are not limited to ordinary administrative delay. They concern HMRC’s assessment of the taxpayer’s behaviour and the reason the return remained outstanding.
Anyone facing an allegation of deliberate behaviour should obtain advice from an appropriately qualified tax professional. Routine bookkeeping support does not replace representation in a tax investigation or penalty dispute.
How quickly late-filing charges can accumulate
A return that remains outstanding for more than six months can attract the initial £100 penalty, up to £900 of daily penalties and a further charge of at least £300.
This means the minimum late-filing penalties can reach £1,300 before considering late payment, interest or a later 12-month filing penalty.
Where the return remains outstanding for more than 12 months, the ordinary minimum filing charges can rise further. The total may be significantly higher where the tax-related percentages produce charges above the £300 minimums.
The cost of delay is therefore not confined to the initial £100 notice. Filing promptly after discovering the problem can prevent later stages from being reached.
Late payment is separate from late filing
Tax shown as payable through Self Assessment is normally due by 31 January following the end of the tax year. A second payment on account may also be due by 31 July.
Late-payment interest begins to accrue from the day after the payment deadline. It is charged according to HMRC’s official late-payment interest rate and continues until the outstanding amount is paid.
HMRC’s late-payment rate can change when the Bank of England base rate changes. From 6 April 2025, the formula used for most late tax payments became the Bank of England base rate plus four percentage points.
The current rate should therefore be checked through HMRC’s late and early payment interest-rate guidance rather than relying on a percentage quoted in an older article.
Late-payment penalties
In addition to interest, Self Assessment tax remaining unpaid can attract late-payment penalties.
The first penalty is generally charged when tax remains unpaid 30 days after the deadline. It is normally 5 per cent of the amount still outstanding at that point.
A further 5 per cent can be charged on tax still unpaid five months after the first penalty date, effectively six months after the original payment deadline.
Another 5 per cent can apply where tax remains outstanding 12 months after the deadline. Each percentage is calculated using the amount still unpaid at the relevant trigger date.
Paying part of the liability before a trigger date can therefore reduce the amount on which the corresponding late-payment penalty is calculated, although interest will still apply to overdue tax until it is paid.
Payments on account and unexpected tax bills
Payments on account are advance Income Tax payments towards the following tax year. They are generally required where the previous year’s relevant Self Assessment liability exceeds £1,000 and less than 80 per cent was collected outside Self Assessment.
The first payment on account is normally due on 31 January and the second on 31 July. Each is usually half the relevant previous year’s liability.
A first Self Assessment bill can therefore be larger than expected because the taxpayer may need to pay the balancing liability for one year and the first payment on account for the next year at the same time.
Payments on account can sometimes be reduced where the taxpayer reasonably expects the following year’s liability to be lower. Reducing them excessively can result in interest when the actual liability is established.
A reduction should be based on a supportable estimate rather than used simply to postpone payment. An appropriately qualified tax adviser can help assess the likely liability.
What to do when you cannot pay HMRC
A taxpayer who cannot pay the full bill should still submit the return by the deadline. Filing prevents late-filing penalties from accumulating even though interest and possible late-payment penalties may continue.
HMRC may agree a Time to Pay arrangement allowing the debt to be paid by instalments. Eligibility and the payment period depend on the amount owed, the taxpayer’s circumstances and their ability to make the proposed payments.
Some taxpayers can establish an arrangement online after filing the return. Others need to contact HMRC directly so that income, expenditure, assets and other debts can be discussed.
HMRC’s guidance on paying a tax bill by instalments explains the available process and information that may be required.
An agreed arrangement can affect late-payment penalties where it is established before the relevant trigger date. Interest normally continues to accrue on the unpaid tax.
What HMRC considers a reasonable excuse
A taxpayer can appeal a late-filing or late-payment penalty where they had a reasonable excuse for failing to meet the obligation.
HMRC considers the individual circumstances. A reasonable excuse is generally an unexpected or unusual event that prevented a normally responsible person from filing or paying on time.
Examples that may be accepted include a serious illness, an unexpected hospital stay, bereavement shortly before the deadline, fire, flood, theft or a significant failure of HMRC’s online services.
Computer or software failure may qualify where it occurred while the taxpayer was preparing the return and reasonable steps had been taken. The taxpayer should retain evidence such as error messages, support correspondence and dates.
HMRC’s current reasonable-excuse guidance provides examples of circumstances that may and may not be accepted.
Reasons HMRC may reject
HMRC does not normally accept that the taxpayer did not receive a reminder. The obligation to file and pay remains with the taxpayer.
Finding the online system difficult is not generally enough by itself. A taxpayer experiencing difficulty should seek assistance before the deadline or consider whether digital-exclusion arrangements are relevant.
A failed payment caused by insufficient funds is not normally a reasonable excuse. A shortage of money may be considered only where it resulted from events outside the taxpayer’s control and the wider circumstances support the claim.
Making a mistake on the return is also separate from having a reasonable excuse for missing the filing deadline.
Reliance on another person, including an accountant or agent, is considered according to the circumstances. HMRC’s public guidance now recognises that reliance may sometimes form part of a reasonable excuse, but the taxpayer must explain what happened and demonstrate that they took reasonable care.
Acting promptly after the excuse ends
A reasonable excuse does not provide an unlimited extension. The taxpayer must correct the failure without unreasonable delay after the circumstances preventing compliance have ended.
Someone who was seriously ill at the deadline but recovered several weeks later should file or pay as soon as reasonably possible after recovering.
Waiting for months after the original problem has ended can weaken the appeal because the later delay may no longer be explained by the same event.
The taxpayer should retain evidence showing the relevant dates, how the event prevented compliance and when action was eventually taken.
How to appeal a Self Assessment penalty
A penalty appeal is usually required within 30 days of the date shown on the penalty notice. The appeal should identify the penalty, explain why it is disputed and include evidence supporting the taxpayer’s position.
An online appeal may be available for the initial £100 late-filing penalty. Other cases may require a written appeal or HMRC’s Self Assessment penalty appeal form.
If the appeal itself is late, the taxpayer should explain both the original reasonable excuse and why the appeal was not made within the normal period.
HMRC may accept the appeal, reject it or offer a review. A taxpayer who remains dissatisfied may be able to ask for an independent review or appeal to the tax tribunal.
The government’s guidance on disputing a tax penalty explains the main appeal routes and deadlines.
Filing an estimated return before the deadline
Where complete information is unavailable, it may sometimes be possible to submit a return containing a reasonable provisional figure and amend it later.
The return should identify that the figure is provisional and explain the basis used. An estimate should not be invented merely to produce a lower liability.
Submitting a supportable provisional return may avoid late-filing penalties, but the taxpayer must replace the estimate with the correct figure when the information becomes available.
Professional advice should be obtained where material records are missing or the correct treatment is uncertain. An inaccurate return can create separate penalties where reasonable care has not been taken.
Penalties for inaccurate tax returns
Late-filing penalties are separate from penalties for submitting an inaccurate return. HMRC can charge an inaccuracy penalty where an error understates tax, overstates a repayment or produces another loss of tax.
The percentage depends partly on behaviour. HMRC distinguishes between failure to take reasonable care, deliberate inaccuracies and deliberate inaccuracies that were concealed.
The penalty can also depend on whether the taxpayer disclosed the error voluntarily before HMRC discovered it and how much assistance was provided in correcting the position.
A genuine mistake does not automatically produce the maximum charge. Maintaining reliable records and seeking advice on uncertain issues can help demonstrate that reasonable care was taken.
Penalties for failing to keep records
Self-employed people and landlords must retain records supporting the income and expenses reported on their returns. HMRC can charge a penalty where adequate records have not been maintained.
Supporting evidence can include invoices, receipts, bank statements, platform reports, tenancy records, mileage logs and calculations used to apportion mixed personal and business costs.
Self-employed records normally need to be retained for at least five years after the 31 January filing deadline for the relevant tax year. Different periods can apply where a return was filed late or HMRC has opened an enquiry.
Digital copies are acceptable where they remain legible, complete and accessible. A photograph of a receipt provides little protection if it cannot be located or matched to the corresponding transaction.
Self Assessment penalties and Making Tax Digital
Making Tax Digital for Income Tax began applying from April 2026 to qualifying sole traders and landlords with gross qualifying income over £50,000, subject to exclusions and exemptions.
Those within the system need to maintain digital records, send quarterly updates and submit their final tax return through compatible software.
HMRC has confirmed that penalty points will not be charged for late quarterly updates during the 2026 to 2027 introductory tax year. The updates still need to be completed before the taxpayer can submit the final return.
The annual tax-return deadline and payment obligations continue to matter. Entering Making Tax Digital does not remove the risk of annual filing, payment and inaccuracy penalties.
Our guide to Making Tax Digital explains the thresholds, digital records and quarterly-update process.
Landlords and Self Assessment penalties
Landlords may need to file Self Assessment returns reporting gross rent, letting-agent deductions, repairs, finance costs and other property transactions.
Waiting for an annual statement from the letting agent does not remove the landlord’s responsibility to meet the filing deadline. Missing statements and unclear deductions should be investigated before January.
Landlords entering Making Tax Digital may also need to maintain digital property records during the year rather than reconstructing income and expenses at the filing deadline.
Our guide to property and landlord bookkeeping explains how gross rent, agent settlements, expenses and individual properties can be organised.
Company directors and Self Assessment
Being a company director does not automatically mean that an individual must file a Self Assessment return. A return may still be required because of untaxed income, dividends, property income, capital gains, the High Income Child Benefit Charge or another reason.
The company’s annual accounts and Corporation Tax return are separate from the director’s personal Self Assessment obligations. Filing one does not complete the other.
Salary should agree with payroll records, while dividends should be supported by the company’s distributable profits, dividend vouchers and appropriate company approvals.
Our guide to director salary and dividends explains why the two forms of payment require different company and personal records.
Directors should confirm their personal filing requirements with an appropriately qualified tax adviser rather than assuming that every director must submit a return or that none do.
Allowable expenses and incomplete returns
Missing expense records can lead to a higher tax bill because legitimate deductions may be omitted. Unsupported estimates can create a different risk if HMRC later asks for evidence.
Before submitting the return, business costs should be reviewed for private use, capital purchases, simplified expenses and amounts paid personally by the owner.
Our guide to allowable expenses explains common claims involving home working, vehicles, travel, equipment and mixed-use costs.
Submitting on time does not require the taxpayer to overclaim. Uncertain or material expenses should be reviewed with an appropriately qualified adviser before inclusion.
Bank reconciliation before filing
Bank reconciliation helps identify income and expenses that have been omitted, duplicated or allocated incorrectly before the tax return is prepared.
Every business bank account, credit card and payment platform should be compared with the accounting records. Unidentified transactions should be investigated rather than posted to a general category solely to complete the return.
Our guide to bank reconciliation explains how regular comparison with bank and payment-provider statements supports more dependable accounts.
Reconciliation does not determine every tax treatment, but it provides stronger evidence that the underlying financial movements have been captured.
Why January bookkeeping creates unnecessary risk
Preparing an entire year of records shortly before 31 January leaves little time to resolve missing invoices, obtain statements or ask for tax advice.
A software problem, illness or delayed response from a third party can then turn an ordinary bookkeeping query into a missed filing deadline.
Monthly bookkeeping spreads the work across the year and makes it easier to identify increasing profit, payments on account and cash that should be reserved for tax.
Our guide to the real cost of DIY bookkeeping explains how owner time, missed expenses and retrospective correction can make delayed bookkeeping more expensive than it first appears.
Preparing well before the Self Assessment deadline
The bookkeeping should ideally be completed soon after the tax year ends rather than postponed until the following January.
Bank accounts should be reconciled, income sources checked and expense documents collected. Capital purchases, finance agreements and private-use calculations should be identified for the accountant or tax adviser.
Preparing early does not make the tax payable earlier than the statutory date. It provides more time to understand the bill and arrange the necessary cash.
Our new tax year bookkeeping checklist explains the records and settings worth reviewing as one tax year closes and another begins.
When outsourced bookkeeping helps prevent penalties
A sole trader or landlord can maintain their own records successfully where transactions remain manageable and the work is completed consistently.
External support becomes more useful where several income sources, accounts, payment platforms, properties or VAT obligations need regular processing.
The service scope should identify who maintains the records, reconciles the accounts and supplies information to the person preparing the tax return. Bookkeeping support does not automatically include tax-return preparation or penalty appeals.
Bookkeeping Packages Ltd provides bookkeeping services for UK businesses, including regular transaction processing and reconciliation according to the agreed scope.
Where responsibility for the continuing monthly workflow needs to be transferred, our outsourced bookkeeping service explains how support can be structured.
To discuss overdue or incomplete bookkeeping records before they affect a filing deadline, use the Bookkeeping Packages enquiry form.
About the Author
Stuart Kerr is Managing Director of Bookkeeping Packages Ltd, an outsourced bookkeeping service supporting UK small businesses and accountancy practices. With over 20 years of bookkeeping experience, Stuart specialises in helping businesses maintain reliable financial records and useful management information.
This article is provided for general information only. Stuart Kerr is a professional bookkeeper, not a tax, legal or regulated financial adviser. Nothing in this article constitutes tax, legal or financial advice or representation in an HMRC dispute. Advice specific to your circumstances should be obtained from an appropriately qualified professional.