Key Accounting Dates March 2026: Important UK Tax Deadlines for Your Business

/Published:20th February 2026/inBusiness, Limited Company, Making Tax Digital, Running a business, Self Employed, Tax
Accounting Wise - Key Accounting Dates March 2026 Important UK Tax Deadlines for Your Business

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Staying ahead of tax deadlines is one of the simplest ways to protect your business from penalties, interest charges and unnecessary stress.

March is a particularly busy month in the UK tax calendar. Whether you run a limited company, manage payroll, submit VAT returns, or operate in construction under CIS, there are multiple compliance dates to keep firmly on your radar.

Below is your guide to the key accounting dates for March 2026, with practical explanations of what each deadline means and how to stay compliant.

1 March 2026 – Corporation Tax Payment – 31 May 2025 Year Ends

If your company’s accounting period ended on 31 May 2025, your Corporation Tax payment is due by 1 March 2026.

Under UK rules, Corporation Tax is payable nine months and one day after the end of your accounting period. Late payment triggers:

  • Interest charges from HMRC
  • Potential penalties
  • Cash flow disruption

Even if your Corporation Tax return is not yet due, the payment must still be made on time.

Tip: Always calculate your Corporation Tax liability well before the deadline so you can plan cash flow accordingly.

Learn more in our guide: “What is a corporation tax return?”

1 March 2026 – Advisory Fuel Rates for Company Car Drivers – New Rates Published

HMRC publishes updated Advisory Fuel Rates (AFRs) each quarter. The new rates typically apply from 1 March.

These rates are used when:

  • Reimbursing employees for business mileage in company cars
  • Calculating fuel benefit charges
  • Charging employees for private fuel use

Using incorrect rates can result in underpayments or overpayments, and potentially benefit-in-kind complications.

If you operate company vehicles, it is important to update payroll systems and expense policies immediately when new rates are published.

7 March 2026 – VAT Return Submission and Payment (Online)

If your VAT period ended on 31 January 2026, your VAT return and payment are due by 7 March 2026.

Under Making Tax Digital rules, VAT-registered businesses must:

  • Submit VAT returns digitally
  • Keep digital records
  • Pay VAT electronically

Missing this deadline can result in:

  • Default surcharge penalties
  • Interest charges
  • A compliance history flag

Tip: Set internal reminders at least 7 days before the deadline to review your VAT position and ensure sufficient funds are available.

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2026 Key Accounting Dates

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19 March 2026  – PAYE, NIC and CIS Payment (Postal)

If you pay by post, this is the deadline for PAYE, National Insurance Contributions (NIC), and CIS deductions for the tax month ending 5 March 2026.

This applies to:

  • Employers operating payroll
  • Construction businesses deducting CIS from subcontractors

Because postal payments can be delayed, electronic payment is generally safer and more reliable.

19 March 2026  – CIS Return – Month to 5 March 2026

Construction Industry Scheme (CIS) returns must be submitted monthly. The return for payments made to subcontractors up to 5 March 2026 must be filed by 19 March 2026.

You must:

  • Declare all subcontractor payments
  • Confirm employment status
  • Verify deduction rates

Late CIS returns attract automatic penalties starting from the first day overdue.

22 March 2026 – PAYE, NIC and CIS Payment (Electronic)

If paying electronically, the deadline for PAYE, NIC and CIS for the tax month ending 5 March 2026 is 22 March 2026.

Most businesses pay electronically via:

  • Direct Debit
  • Faster Payments
  • BACS

Ensure cleared funds reach HMRC by this date to avoid interest charges.

31 March 2026  – Corporation Tax Returns – 31 March 2025 Year Ends

If your company’s accounting period ended on 31 March 2025, your Corporation Tax return must be filed by 31 March 2026.

This deadline is separate from the payment deadline, which would have been due earlier (1 January 2026).

The return must:

  • Be filed online with HMRC
  • Include statutory accounts
  • Include a completed CT600
  • Be submitted in iXBRL format

Late filing penalties start immediately and increase the longer the delay continues.

31 March 2026  – Annual Tax on Enveloped Dwellings (ATED) – Amend Returns

If your company owns UK residential property valued above the ATED threshold, and an ATED return was filed for the year to 31 March 2025, this is the deadline to amend that return.

ATED applies to certain properties held within companies and other corporate structures.

Failure to comply can result in significant penalties, so professional review is strongly recommended if your business holds high-value residential property.

Why March Is a High-Risk Month for Penalties

March combines multiple deadlines across:

  • Corporation Tax
  • VAT
  • PAYE
  • CIS
  • ATED

Because many of these fall close together, it is easy for something to be missed, particularly if you manage accounting internally.

A missed deadline can mean:

  • Immediate penalties
  • HMRC interest
  • Increased compliance scrutiny

This is why structured planning and digital accounting systems are critical.

How to Stay Ahead of March 2026 Deadlines

To keep your business compliant:

  1. Maintain accurate digital bookkeeping throughout the year
  2. Review your tax liabilities at least one month before deadlines
  3. Set automated calendar reminders
  4. Reconcile payroll and CIS records monthly
  5. Ensure Corporation Tax forecasts are updated regularly

Working with a proactive accountant means you are reminded before problems arise, not after penalties land.

Final Thoughts on March 2026 UK Accounts Deadlines

March 2026 is packed with important UK tax deadlines. From Corporation Tax payments and returns to VAT, PAYE, and CIS obligations, it is a month that requires careful planning and accurate record keeping.

If you are unsure about any upcoming deadline or want to ensure your business stays compliant and efficient, professional support can make a significant difference.

At Accounting Wise, we help UK limited companies, contractors and growing businesses stay on top of every accounting date, so nothing is left to chance.

If you would like tailored accounting support for your business in 2026, our team is here to help.

Need help with your accounts? Contact Accounting Wise Today!

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