Key Accounting Deadlines UK 2026: The Ultimate Startup Guide

As startup founders, you’ve got a million and one things on your to do list. But, staying compliant with accounts filing deadlines throughout the year is non-negotiable.  

In this post, we’ll guide you through the most important accounting deadlines UK startups need to be aware of. Here’s a quick snapshot:

Read on for a detailed explanation of each, including tips and examples to help you make sense of what’s required of your business.  

1. Annual Accounts Filing Deadline 

One of the most important accounting deadlines you’ll face is the filing of your year end accounts with Companies House. Your company’s first annual accounts must be submitted within 21 months of the date of incorporation. After this, annual accounts must be filed every year within 9 months of the company’s financial year-end.   

Example: Company A was incorporated on 1st January 2025. This means its first set of annual accounts, assuming they ends on 31st December 2025, must be submitted by 30th September 2026. 

From the second year onwards, assuming the financial year-end is 31 December 2026, the next annual accounts deadline will be 30 September 2027 (9 months after the financial year-end). 

Why It Matters: 

• Missing the annual accounts filing deadline can result in penalties ranging from £150 to £1,500 depending on how late the accounts are submitted. 
• Filing accounts late for two consecutive years increases the penalty amount, so staying on top of these deadlines is crucial. 

Tip: Start preparing your financial statements early, and make sure your bookkeeping is up-to-date throughout the year to avoid last-minute panic when the deadline approaches. For a detailed breakdown of what’s required, see our guide Limited Company End-of-Year Accounts: A Comprehensive Guide. 

2. Corporation Tax Return & Payment Deadline 

Another key deadline for UK startups is filing the Corporation Tax Return (CT600). This must be submitted to HMRC within 12 months of the end of your financial year even if your company made no profit or owes no tax. This deadline is critical when paying corporate tax. 

For limited companies, you can often file your annual accounts with Companies House at the same time as submitting your Corporation Tax Return to HMRC.  

BUT 

If your company owes Corporation Tax, the payments must be made within 9 months and 1 day after the end of the accounting period.   

This means you need to calculate your tax liability well before the filing deadline.  

Example: Company A was incorporated on 1 January 2025 and has a financial year-end of 31 December 2025.  

It must: 

• Pay any Corporation Tax owed by 1 October 2026 (9 months + 1 day after year-end) 

• Submit its CT600 by 31 December 2026 (12 months after year-end) 

Why It Matters: 

If you miss your filing deadlines, penalties increase the longer your return remains overdue: 

• 1 day late: £100 penalty
• 3 months late: Another £100 penalty 
• 6 months late: HMRC estimates your Tax bill and adds a 10% of the unpaid tax 
• 12 months late: An additional 10% of any unpaid tax 

If your tax return is late three times in a row, the £100 penalties increase to £500 each.  

If it remains more than 6 months overdue, HMRC will issue a tax determination. This is an estimate of the Corporation Tax they believe you owe and you cannot appeal it. 

You must still file your return, after which HMRC will recalculate the tax, interest and penalties due.  

Tip: Align the preparation of your Corporation Tax Return with your annual accounts to streamline the process and avoid missing either deadline. 

3. Confirmation Statement Filing Deadline 

In addition to submitting annual accounts, UK companies must file a Confirmation Statement with Companies House at least once every 12 months. This document verifies that your company information is up-to-date, including details of directors, registered office address and shareholders. 

Why It Matters: 

The deadline to submit your Confirmation Statement is 12 months after the last one was filed or 12 months after incorporation for new companies and you must file it within 14 days of this date. 

Failing to submit your Confirmation Statement on time can result in your company being struck off the Companies House register, meaning your startup could be dissolved.  

Example: Company A would submit a new one every year on January 1st. 

Tip: Set a reminder a few weeks before your Confirmation Statement is due and review your company’s details carefully to ensure all information is accurate and up-to-date.   

4. VAT Returns and Payment Deadlines 

If you’re startup is VAT-registered, you’ll need to file VAT returns either quarterly, monthly, or annually depending on your registration. Most startups will file quarterly, with the VAT return and payment due 1 month and 7 days after the end of the accounting period. 

You don’t have to register for VAT immediately. Registration is required only when your taxable turnover hits (or is expected to hit) £90,000 within 12 months. You can also register voluntarily even if you haven’t reached this threshold.  

Read Registering for VAT as a limited company: A complete guide for a full breakdown.

Example: Company A took a couple of years to hit the VAT threshold but are now registered and submit quarterly in line with their financial year:  

Q1: 1st April 2026 to 30th June 2026 

VAT Return and Payment Deadline: 7th August 2026 (1 month and 7 days after quarter-end) 

Why It Matters: 

Late VAT returns can result in penalties even if there is no VAT to pay. Under HMRC’s penalty system: 

• Each late VAT return counts as one penalty point including nil returns where there is nothing to declare. 
• Once you reach your penalty point threshold, HMRC issues a £200 penalty. The threshold depends on whether you file monthly, quarterly or annually. 
• Continuing to submit returns late after reaching the threshold incurs an additional £200 penalty for each late submission. 

Digital record-keeping is mandatory under Making Tax Digital (MTD) rules so ensure your VAT submissions are compliant with these regulations.   

Tip: Use accounting software that integrates VAT reporting and payment reminders to stay on top of these deadlines. 

5. PAYE and Payroll Deadlines 

If you employ staff, your UK startup must also meet PAYE (Pay As You Earn) and payroll deadlines. Payroll information needs to be submitted to HMRC every time you pay your employees through a Full Payment Submission (FPS). 

Payments for PAYE must be made: 

• By the 22nd of the following month if paying electronically (recommended)  

• By the 19th if paying by post  

Why It Matters:

Missing PAYE deadlines can result in penalties and cause complications with HMRC. While the first late payment in a tax year does not count as default, repeated late payments quickly become costly.  

HMRC applies penalties based on how often payments are late within the same tax year:  

• 1 to 3 late payments: 1% of the amount paid late 

• 4 to 6 late payments: 2% 

• 7 to 9 late payments: 3% 

• 10 or more late payments: 4% 

Interest is charged daily on all unpaid amounts from the payment due date until the balance is cleared.  Additional penalties apply if PAYE is not paid in full. 

The rates are:  

• After 6 months: 5% of the outstanding amount 
• After 12 months: a further 5% of the outstanding amount
   

These additional penalties can apply even if only one payment in the tax year is late.  

Late or incorrect payroll submissions can also affect employee tax records which can lead to confusion and disputes in your company. 

Tip: 

• If your startup is struggling with deadlines or unsure about the filing process, professional help can make a big difference.
• Consider outsourcing payroll to an accountant or using reliable payroll software to ensure timely submissions and payments. 

Rise Accounting specialises helps startups stay compliant and meet accounts filing deadlines with ease through expert accounting and bookkeeping services.

Get in touch today to find out how we can help you stay on top of your accounting obligations.