Every January, the same pattern repeats across UK practices: partners working weekends, junior staff drafting returns late into the evening, and SA100, CT600 and CGT prep support becoming the thing that decides whether the season is merely busy or genuinely unsustainable. The workload itself doesn’t have to change, but who does the preparation work, and how early it starts, makes the difference between a controlled season and a burnt-out team.
This guide looks at where the SA100, CT600 and CGT prep workload actually piles up, what can be safely handed off ahead of the January rush, and how practices are restructuring the season without sacrificing quality.
Why Self-Assessment Season Hits Practices So Hard
The problem isn’t really the SA100 return itself; it’s that self-assessment, corporation tax, and capital gains work all land in overlapping windows, competing for the same small pool of qualified staff. A practice with fifty personal tax clients and a handful of corporation tax year-ends in the same quarter is effectively running three filing seasons at once.
Where the Time Actually Goes
Very little of the time spent on SA100, CT600 and CGT preparation is genuinely technical. Most of it sits in tasks like:
- Chasing clients for missing documents
- Entering figures from bank statements and dividend vouchers
- Reconciling prior-year data
- Assembling supporting schedules
All of that happens before an accountant ever needs to apply judgement to the return. That preparation stage is exactly where outsourced support has the most impact.
Separating Preparation Work from Review Work
What Preparation Covers
- Data collection and document chasing
- Bookkeeping tie-outs against bank records
- Draft population of the return
What Stays With the Accountant
- Treatment decisions
- Reliefs claimed
- Final review and submission
A Worked Example
A practice with 80 self-assessment clients might have an administrator collect P60s, dividend vouchers, and bank interest certificates through October and November, populate draft returns in the practice’s software by mid-December, and flag any gaps to clients well before Christmas. The accountant then reviews and finalises each return in January, rather than starting the whole process from a blank page. This mirrors the split used for bank reconciliations and payroll prep, where the recurring, rules-based work is handled separately from anything requiring professional judgement.
Starting Earlier Without Adding Headcount
Most of the January crunch is really an October-to-December problem: client data that could have been collected months earlier gets left until the deadline is close. A practice that builds document collection into its client onboarding process and chases outstanding information from autumn onward removes a large share of the pressure before the season even starts.
People Also Ask About SA100, CT600 and CGT Preparation
What’s the deadline for filing a UK self-assessment return?
The online self-assessment deadline is 31 January following the end of the tax year, with a paper filing deadline of 31 October.
When is CT600 due?
A CT600 corporation tax return is due 12 months after the end of the company’s accounting period, though the tax itself is normally due 9 months and 1 day after the period ends.
Do I need to report capital gains separately from my self-assessment?
UK residential property gains often need reporting within 60 days of completion through HMRC’s capital gains tax service, in addition to being included on the annual self-assessment return.
Can preparation work for tax returns be outsourced safely?
Yes, provided the split between preparation and professional review is clearly defined; the outsourced team handles data entry and document chasing, while the qualified accountant retains full control over treatment decisions and final sign-off.
How Virtual Service Assists Supports Filing Season
We handle the preparation side of SA100, CT600 and CGT support, so your qualified staff spend filing season reviewing and advising rather than typing figures into a return. See our guide to outsourced back-office support cost for how this is typically priced.
Getting Started
If this filing season is already looking like the last one, get in touch before the busiest weeks hit.
