Tax Returns: A Compliance Reference for Accountants and Tax Professionals

With MTD for Income Tax replacing traditional self-assessment tax returns, and basis period reform reshaping how trading income is allocated to tax years, there’s a lot in motion for practices managing compliance for tax returns across a mixed client base.

This page brings together the key return types, filing obligations and deadlines you need to stay on top of – including a practical summary of what the incoming changes mean for your clients.

Return Types at a Glance

The way a business is structured will impact its tax returns, and it’s important to understand the differences. In most cases, you’ll be working with one of the two main tax return types: self-assessment for individuals and corporation tax returns for companies.

Self-Assessment: SA100 and Supplementary Pages

Individuals – including sole traders, partners, and anyone with income outside PAYE – file via self-assessment using Form SA100 as the core return. The SA100 is then supplemented by additional pages, depending on the taxpayer’s circumstances.

Practitioners should be familiar with these supplementary pages in particular, as they’re the ones you’ll come across most often:

• SA102: Employment income and company directors
• SA103S/SA103F: Self-employment (short and full versions)
• SA105: UK property income
• SA108: Capital gains

A full list of supplementary pages is available from HMRC, and getting the right pages in from the start saves time filing amendments down the line, as well as minimising compliance risk for clients.

Corporation Tax Returns: CT600 and Supplementary Pages

Companies file CT600 corporation tax returns, typically alongside a tax computation and a copy of the statutory accounts for the period. Again, supplementary pages are required for specific circumstances. The two main types are:

• CT600A: Close company loans to participators
• CT600C: Group relief claims

A trading company must file a corporation tax return even when it’s loss-making and has no tax to pay. The filing obligation doesn’t go away just because the tax bill does, and failure to file remains a compliance risk regardless of the tax position.

Determining Self-Assessment Obligations

Clients already in self-assessment will receive a Notice to File from HMRC each tax year. However, it’s worth keeping an eye on those whose circumstances have recently changed – particularly where new income streams have arisen during the year.

Common triggers for self-assessment registration include:

• Self-employment or partnership income
• UK property income
• Dividend or interest income outside the standard allowances
• Total income over £100,000 (loss of personal allowance tapering)
• Capital gains above the annual exempt amount

For borderline cases, HMRC’s self-assessment eligibility tool offers a quick way to confirm whether a client needs to file.

Filing Deadlines: Quick Reference

Remember that payment deadlines run separately from filing deadlines for both income tax and corporation tax. Make sure clients are briefed separately for their payment on account obligations and corporation tax payment due dates to avoid interest and penalties.

Making Tax Digital for Income Tax: Action Checklist for Practices

MTD for Income Tax applies to anyone in self-assessment with qualifying income, from self-employment and/or property, above £10,000. Under MTD, the traditional annual self-assessment return is replaced by quarterly updates submitted via MTD-compatible software, followed by a final declaration.

Practices should be working through the following now:

• Identify clients with qualifying income above £10,000
• Confirm MTD-compatible software is in place, or start evaluating options
• Establish a workflow for submitting quarterly income and expense updates
• Prepare clients for what the new process looks like for them

Our tax return software is MTD-ready and built to support quarterly update workflows. Get in touch to find out more about readiness planning for your client base.

Basis Period Reform: What It Means for Your Clients

HMRC is moving to a tax year basis for allocating trading income, replacing the current year basis rules. In practice, this mainly affect clients who don’t draw up accounts to 31 March or 5 April, and those in the early years of trading.

If you have clients on non-standard year-ends, now is a good time to model the transition impact and explore whether a year-end change makes sense before the reform lands.

Take Care of Tax Returns with IRIS

Tax return compliance means staying ahead of the obligations, deadlines, and legislative changes that affect your clients before they become problems. With MTD for Income Tax and basis period reform both on the horizon, now is a good time to review your workflows and make sure your software is doing the heavy lifting.

If you’d like to see how IRIS can support your practice across SA, CT600, and MTD submissions, explore our tax return solutions or get in touch with the team.