Important Accounting Dates September 2026

September is a busy month in the compliance calendar. Between quarterly VAT returns, monthly payroll obligations, corporation tax payments and returns, and a handful of less familiar deadlines like the Economic Crime Levy, there is plenty for business owners, directors and employers to keep on top of. Miss one and you risk interest charges, penalties, or at worst a compliance investigation from HMRC.

Our September 2026 article looks at some of the key accounting and tax deadlines for the month, explains who each one applies to, and offers practical advice on staying compliant. Whether you run a limited company, operate a payroll, or manage VAT-registered trading, use this as your month-at-a-glance reference.

Who this applies to

The deadlines below are relevant to a broad range of UK businesses and their advisers, including:

• Limited company directors with corporation tax payments and returns falling due
• Employers running PAYE payroll and reporting through Real Time Information (RTI)
• VAT-registered businesses submitting returns under Making Tax Digital
• Contractors and subcontractors operating within the Construction Industry Scheme (CIS)
• Larger entities caught by the Economic Crime (Anti-Money Laundering) Levy
• Businesses with company car drivers claiming or repaying fuel costs

Exact dates depend on your accounting period, VAT quarter and payroll cycle, so always check your own filing and payment obligations against your records.

September 2026 tax deadlines at a glance

Here is the full list of key dates for the month, in date order.

1 September: Corporation Tax payment for 30 November 2025 year ends

Corporation tax is due nine months and one day after the end of your accounting period. For companies with an accounting period ending on 30 November 2025, the payment deadline is 1 September 2026. Note that the payment falls due before the return itself, which is not needed until 30 November 2026. You must therefore calculate and pay your liability even though the CT600 return has not yet been filed.

Payment should be made electronically. Allow time for it to clear, as HMRC treats the payment as made on the date it reaches their account, not the date you initiate it. You can find current payment methods and processing times on the GOV.UK guide to paying Corporation Tax.

1 September: Advisory Fuel Rates updated

HMRC reviews and publishes its Advisory Fuel Rates (AFRs) four times a year, on 1 March, 1 June, 1 September and 1 December. New rates take effect from 1 September 2026. These rates apply only to employees using a company car, either to reimburse them for business mileage or to work out how much they must repay for private fuel.

If you pay no more than the published rate, there is no taxable profit and no Class 1A National Insurance to account for. You can continue using the previous quarter’s rates for up to one month after the new figures take effect, which gives payroll teams time to update their systems. Check the latest figures on the GOV.UK Advisory Fuel Rates page once published.

7 September: VAT return and payment for quarter ending 31 July 2026

Businesses with a VAT quarter ending 31 July 2026 must submit their return and pay any VAT due by 7 September 2026. This applies to online submissions, which under Making Tax Digital is now the standard route for almost all VAT-registered businesses.

Remember that the payment must reach HMRC by the deadline, not simply be initiated. If you pay by Direct Debit, HMRC collects the amount automatically a few working days after the submission deadline, so ensure your return is filed in good time. See the VAT return deadlines guidance for confirmation of your dates.

19 September: PAYE, NIC and CIS payment (postal) for month-end 5 September 2026

Employers who still pay HMRC by cheque through the post must ensure their PAYE, National Insurance and CIS deductions for the tax month ending 5 September 2026 reach HMRC by 19 September. Postal payments carry an earlier deadline than electronic ones, and cheques are increasingly discouraged, so most employers will find it simpler and safer to pay electronically.

19 September: CIS return for the month to 5 September 2026

Contractors operating within the Construction Industry Scheme must file their monthly CIS return by 19 September 2026, covering payments made to subcontractors in the month to 5 September. The return is due even if you have made no payments in the period, in which case you must submit a nil return or notify HMRC that no return is due. Late CIS returns attract automatic penalties starting at £100, so this is one to diarise carefully.