UK Tax Deadlines Small Businesses Cannot Miss

A missed deadline can be more expensive than the tax bill itself. For a cab driver finishing a long shift, a subcontractor moving between sites, or a landlord dealing with a repair, tax admin is easy to put off. But UK tax deadlines do not move because work is busy. Knowing what is due, when it is due and what records you need gives you far more control over your cash flow and keeps avoidable HMRC penalties at bay.

The dates that apply to you depend on how you trade. A sole trader will have different responsibilities from a limited company director, while CIS contractors, VAT-registered businesses and employers have extra reporting dates to manage. The key is to treat tax as a regular business cost, not an annual surprise.

The main Self Assessment tax deadlines

Self Assessment applies to many self-employed workers, landlords, company directors and people with income that has not been taxed through PAYE. The tax year runs from 6 April to 5 April, which is why deadlines can feel out of step with the calendar year.

For the tax year ending 5 April 2026, these are the dates to keep in your diary:

• 5 October 2026 - register for Self Assessment if you are newly self-employed or have another reason to file and have not previously sent a return.

• 31 October 2026 - deadline for a paper tax return.

• 30 December 2026 - deadline to file online if you want HMRC to try to collect tax under £3,000 through your PAYE tax code, where eligible.

• 31 January 2027 - deadline for online Self Assessment returns and for paying the balancing tax bill for 2025/26.

• 31 July 2027 - second payment on account, where payments on account apply.

The 31 January date catches people out because it is both a filing deadline and usually a payment deadline. Filing your return early does not mean you must pay early, but it shows you what is due and leaves time to plan. It can also prevent a rushed return where legitimate expenses, such as mileage, tools, protective clothing, accountancy fees or a proportion of home-working costs, are missed.

Payments on account: why January bills can feel high

If your Self Assessment bill was more than £1,000 and less than 80% of your tax was collected at source, HMRC will normally ask for payments on account towards the following year. Each payment is usually half of the previous year’s tax and Class 4 National Insurance bill.

This means the payment due on 31 January may include your balancing payment for the last tax year plus the first instalment towards the next one. The second instalment falls on 31 July. It is not a duplicate charge, but it can still create a real cash-flow squeeze, particularly after a quieter period or a year with higher earnings.

If you know profits will be lower, you may be able to reduce payments on account. That decision needs care. Reduce them too far and HMRC can charge interest when the final position is calculated. A sensible forecast based on current income and expenses is much better than simply guessing.

Corporation Tax deadlines for limited companies

Running a limited company adds another layer of deadlines. Your company’s accounting period is not always the same as the tax year, so the dates are based on your year end rather than 5 April.

Corporation Tax must usually be paid nine months and one day after the end of your accounting period. For example, a company with a 31 March year end would normally need to pay its Corporation Tax by 1 January of the following year.

Your Company Tax Return, known as a CT600, is normally due 12 months after the end of the accounting period. Although the filing deadline is later than the payment deadline, waiting until then is rarely helpful. You need accurate accounts to calculate the tax owed, and late payment interest can build from the payment due date.

Company directors should also remember that Corporation Tax is separate from personal tax. Salary, dividends, benefits and money taken from the business can all have different tax treatment. The company may be up to date while the director’s own Self Assessment return is still overdue.

VAT deadlines and Making Tax Digital

Most VAT-registered businesses submit VAT Returns under Making Tax Digital rules. For many businesses on quarterly VAT accounting, the return and payment are due one month and seven days after the end of the VAT period. A return for the quarter ending 31 March, for instance, will generally be due by 7 May.

The exact date can vary if you use the Annual Accounting Scheme or another VAT arrangement. If you pay by Direct Debit, set it up early enough for HMRC to collect the payment - normally at least three working days before the deadline.

VAT is especially important to keep separate from day-to-day spending. It is money collected on behalf of HMRC, not extra profit. Putting a percentage of each VAT-inclusive payment into a separate pot can prevent the familiar problem of a healthy bank balance that disappears when the VAT bill arrives.

Digital records also matter. Under Making Tax Digital, most VAT-registered businesses need compatible software or a suitable digital record-keeping process. A spreadsheet may be workable in some circumstances, but the records and VAT submission process still need to meet HMRC requirements. The right approach depends on the size and complexity of the business, but leaving digital bookkeeping until the filing week creates unnecessary risk.

PAYE and CIS deadlines for employers and contractors

If you employ staff, including a director on a salary, PAYE reporting happens every time you run payroll. A Full Payment Submission must normally be sent to HMRC on or before payday. PAYE tax and National Insurance are generally due by the 22nd of the following tax month when paying electronically, or by the 19th if paying by post.

For construction businesses operating the Construction Industry Scheme, a CIS monthly return is normally due by the 19th of each month, covering deductions made from subcontractors in the previous tax month. Any CIS deductions due to HMRC are generally payable by the 22nd when paid electronically.

These dates matter even when there is nothing to report. If no payments have been made to subcontractors, a contractor may need to tell HMRC that no return is due. Ignoring the system can trigger automatic penalties and creates more work later when records need to be put right.

For subcontractors, keep every deduction statement. These show the CIS tax withheld from your payments and are vital when preparing your Self Assessment return or claiming a CIS refund. A missing statement does not always mean the deduction is lost, but resolving it takes time and evidence.

How to stay ahead without living in your bookkeeping

The simplest way to manage deadlines is to build a short monthly routine. Keep business income and expenses recorded as they happen, photograph or upload receipts before they disappear, reconcile your bank transactions, and set aside money for tax. For many sole traders, a weekly 20-minute check is easier than trying to rebuild a year’s records in January.

Use a separate business bank account where possible, even if you are not legally required to have one. It makes trading income, fuel, materials, software, insurance and other costs easier to identify. For landlords, keeping property income and expenses clearly separated can make a major difference when working out taxable profit.

Also keep an eye on changes in your business. Taking on staff, registering for VAT, incorporating a sole trade, buying a property, selling an asset or moving into CIS contracting can all change the deadlines and records that apply. The right tax treatment is rarely something to sort out after the event.

Short And Sons Accountants works with self-employed people, landlords, CIS subcontractors and limited companies who need their compliance handled clearly and practically. Whether your records are already in good order or you are trying to catch up, early action gives you more options than a last-minute return.

A tax deadline is not just a date in a diary. It is a prompt to check that your records, cash reserves and plans still match the business you are actually running.