Help Centre · Self Assessment (Beta) · 2 min read

Self Assessment tax returns in Tax Optimiser (beta)

Prepare and file full SA100 Self Assessment returns for clients not in MTD — with a live tax calculation — from inside Tax Optimiser. Beta access via support@taxoptimiser.co.uk.

Tax Optimiser Updated 3 Jul 2026
Beta feature — Self Assessment tax returns are currently in beta and are switched on for one accountant firm at a time. To gain access for your firm, email support@taxoptimiser.co.uk and the team will enable it and help you get started.

Tax Optimiser can now prepare and file the full Self Assessment tax return (the SA100 and its supplementary pages) for individual clients who are not in Making Tax Digital — the traditional annual return, filed to HMRC through their online channel. You enter the return box by box, watch the tax calculation build live, download an SA302-style calculation for the client, and submit to HMRC without leaving Tax Optimiser.

How this differs from the MTD ITSA screens

Tax Optimiser’s MTD ITSA screens are for clients in Making Tax Digital: digital records, quarterly updates, and HMRC doing the tax calculation. The Self Assessment screens are for everyone else — clients below the MTD threshold or not yet mandated, who still file one annual return. Because the traditional channel has no HMRC calculation service, Tax Optimiser calculates the tax itself, live as you type, so you always see the position before anything is filed. Both features can be used side by side across your client base.

The Self Assessment screen: return sections on the left, the live SA302 calculation with box references and the Download SA302 PDF button

What is supported today

The beta supports tax year 2025-26 (6 April 2025 to 5 April 2026) with the pages most returns need:

  • Employment (SA102) — any number of employments
  • Self-employment, short and full (SA103S / SA103F)
  • UK Property (SA105)
  • Interest & dividends, state benefits and pensions, other UK income
  • Tax reliefs — pension contributions, Gift Aid, Marriage Allowance, Blind Person’s Allowance, the High Income Child Benefit Charge
  • Student and postgraduate loans

Partnership (SA104), Foreign (SA106), Trusts (SA107), Capital Gains (SA108), Residence (SA109) and Additional Information (SA101) pages are on the roadmap — they show as “coming soon” in the section picker, and the calculation tells you clearly if a return needs a page that is not yet supported.

Getting access

The feature is enabled per accountant firm while in beta. Email support@taxoptimiser.co.uk from your firm’s account and the team will switch it on, walk you through the first return, and agree when live filing is enabled for your firm. Feedback during beta directly shapes what gets built next.

Next: Getting started with a client’s return.

The short version

Self Assessment tax returns in Tax Optimiser (beta) — in brief

Tax Optimiser now prepares and files traditional Self Assessment (SA100) returns for individual clients who are not in Making Tax Digital.

The tax calculation is computed live inside Tax Optimiser as you enter the return, because HMRC's traditional channel has no calculation service.

The beta covers 2025-26 with employment, self-employment, UK property, savings and dividend income, reliefs and student loans; more pages are on the roadmap.

Access is per accountant firm during beta - email support@taxoptimiser.co.uk to be switched on.