The Self Assessment dates
For the 2025/26 tax year, tell HMRC by 5 October 2026 if you need to register. The usual paper-return deadline is 31 October 2026; the online deadline is 31 January 2027. The balancing payment for 2025/26 and first payment on account for 2026/27 are also due on 31 January 2027. The second payment on account is due on 31 July 2027. A late notice to file or other exceptional circumstances can change the filing date, so check the notice.
Failure to notify HMRC is separate from filing a return late. The amount of any failure-to-notify penalty depends on tax unpaid by the relevant date, behaviour and disclosure. It is not an automatic maximum charge on 6 October. Register promptly if you have missed the date.
Late filing under the existing rules
For returns still under the existing regime, the first late-filing penalty is £100. After three months, daily penalties of £10 can run for up to 90 days. At six months, another £300 or 5% of the tax due applies, whichever is higher; a further £300 or 5% applies at twelve months, with higher tax-based penalties possible for deliberate withholding. Even a nil-tax return can attract the fixed minimum charges.
A £20,000 liability with all ordinary stages charged gives £100 plus £900 plus £1,000 plus £1,000: £3,000 in filing penalties. Payment penalties and interest are separate. These existing rules still apply to the 2025/26 return due on 31 January 2027, even if you started Making Tax Digital (MTD) for Income Tax in April 2026.
Late payment under the existing rules
The usual balancing-payment penalties are 5% after 30 days, another 5% at six months and a further 5% at twelve months, based on tax still unpaid at each trigger. Payments on account carry interest from their own due dates. Under this older regime, unpaid amounts can be included in the tax balance tested after the balancing-payment deadline for that tax year; they do not receive a separate 5% penalty 30 days after each advance instalment date.
The MTD submission and payment rules
There are no late-quarterly-update penalty points for the 2026/27 tax year. You must still keep records and send the updates before submitting the tax return. From 2027/28 quarterly deadlines count; tax-return deadlines also count. Four points trigger a £200 penalty, followed by £200 for each further missed submission deadline while at the threshold. Only one point arises per deadline even if several businesses have late updates.
Below four points, each point normally expires after 24 months. At four points, expiry alone does not reset the record: you need twelve months of on-time submissions and all outstanding updates and returns for the previous 24 months. The Income Tax points record is separate from VAT.
For late payment of 2026/27 tax under the new regime, the rates are 3% of the amount unpaid at day 15, another 3% of the amount unpaid at day 30, and 10% a year accruing daily from day 31. For 2027/28 tax, the two fixed rates become 4% each; the daily-accruing rate remains 10% a year. The latter charge can run for up to two years. Interest is additional. New-regime payment penalties do not apply to payments on account.
The first year under the new payment penalties has a one-off easement: pay in full or contact HMRC to arrange a payment plan within 30 days to avoid the initial penalty, provided a plan is agreed and followed. If the bill remains unpaid after day 30 without a qualifying arrangement, both day-15 and day-30 amounts enter the calculation. After that first year, the initial period is fifteen days.
The quarterly-update easement is specifically for 2026/27. It is different from the one-off payment easement and does not restart for someone joining MTD in 2027/28. The government has also announced the new penalty regime for other personal Self Assessment taxpayers from April 2027; the MTD four-point threshold should not be applied to annual-only filers.
Interest continues while tax is unpaid
HMRC charges late-payment interest from the tax due date, including on late payments on account. The rate is Bank Rate plus four percentage points, and it can change during the debt period. Use the rates applying over the actual dates instead of assuming one fixed annual percentage. Interest on a penalty starts from that penalty payment due date. Self Assessment late-payment interest is not deductible against future profits.
Repayment interest uses separate rules and a lower rate, normally Bank Rate minus one percentage point with a 0.5% minimum. It is not compensation for all time HMRC has held money. Check the statutory start date for the type of repayment.
Appealing a penalty
An appeal is normally due within 30 days of the notice. Check whether the return, payment date or penalty calculation is wrong, or whether an exception applies. A reasonable excuse may include serious illness, bereavement, loss of records, postal disruption or a computer or software failure that prevented compliance. Keep evidence and explain the dates and steps taken to resolve it.
HMRC considers the circumstances; a software problem is not automatically rejected because it occurred outside HMRC systems. Reliance on an adviser does not automatically excuse a missed obligation, but the care you took can be relevant. Follow the notice about review, appeal and payment or postponement options, and submit the overdue return promptly once able.
If you need time to pay
Contact HMRC as soon as you know you cannot meet a payment. Use its online eligibility checker to see whether you can arrange monthly instalments online. Have your tax reference, bank details and income and spending figures ready. If you cannot use the online service, contact HMRC to discuss an affordable arrangement.
A plan does not always need to be agreed before 31 January to prevent penalties. Under the existing regime, an acceptable arrangement made on or before the relevant penalty trigger can prevent penalties during the arrangement. Under the new regime, an agreed and maintained plan pauses penalties from the date you contacted HMRC. Interest continues, and breaching the plan can restore penalty exposure.
Official sources
Checked 6 September 2026: Self Assessment penalties, MTD penalties and transition, legacy payment penalty dates, appeal grounds and payment plans.