A trusted partner to ease your Self Assessment workload, with precision, care, and experience
As your trusted accounting outsourcing partner, Affinity Outsourcing helps accountancy firms overcome resource bottlenecks and scale effortlessly through expert accounting solutions tailored for your practice.
Why accountancy firms need to outsource Self Assessment tax services
Why would I outsource Self Assessment when my team already does it? For many accountancy firms, tax season is more than just busy; it’s intense. Filing hundreds of SA100 returns on time and with complete accuracy demands constant focus, which drains the accountants.
Soon, Making Tax Digital for Income Tax Self Assessment (MTD for ITSA) will raise the stakes even further, adding four extra quarterly submissions for many clients and turning an already demanding period into a year-round challenge.
That’s why so many accountants tell us they’re facing:
Too much work, not enough hours
Tax season consumes every spare moment, pulling your team away from advisory and client growth.
Constantly changing rules
From allowable expenses to MTD requirements, keeping up is practically a full-time job.
MTD for ISTA pressure
Quarterly updates, digital record-keeping, and year-end returns all need to be perfect, every time.
High stakes
One missed deadline or error risks HMRC penalties and unhappy clients.
Staff burnout
The seasonal rush, late nights, and last-minute submissions take a toll on even the most resilient teams.
Lost opportunities
When your team is buried in admin, they can’t focus on higher-value, revenue-generating work.
Our Self Assessment outsourcing service lifts this burden so you can meet deadlines without losing sleep or affecting your team’s morale.
How does outsourcing solve these challenges?
At Affinity Outsourcing, we step in as your extended tax team during your busiest months, or all year round if you want a completely hands-off Self Assessment process.
We’re not just here to “help”; we take ownership, delivering speed, precision, and full HMRC and MTD for ITSA compliance so you never have to worry about a deadline slipping.
Here’s what we bring to the table:
- Handle the heavy lifting - from collecting client data to final submission, we take care of it all.
- Tackle complexity with confidence - multiple income streams, property portfolios, capital gains… no problem.
- Stay ahead of MTD for ITSA - we manage quarterly updates, keep digital records compliant, and handle the year-end return so you’re always on track.
- Boost your capacity instantly - free your team to focus on advisory, not admin.
- Eliminate bottlenecks - every return filed on time, no matter the season’s pressure.
By outsourcing bookkeeping to us, your practice gains efficiency, reliability, and more hours in the week to focus on strategic advisory services without compromising quality or client satisfaction.
What’s included in our Self Assessment tax outsourcing services
Gathering and reviewing client data
We collect and carefully review all necessary client documentation, including income records, business expenses, bank statements, and any additional relevant information to ensure nothing is missed.
Income source breakdown and categorisation
Our team identifies and categorises multiple income streams such as employment, self-employment, dividends, property income, and capital gains to prepare an accurate Self Assessment return.
Business and property expense review
We perform a detailed review of allowable expenses for sole traders and landlords, helping you maximise your clients’ tax efficiency.
Pre-filing calculations and tax estimations
Before filing, we deliver a clear tax calculation summary so your firm can review and advise clients accordingly.
Supplementary page completion
We prepare fully compliant SA100 forms along with relevant supplementary pages such as SA103, SA105, or SA108, depending on the client’s profile.
Client queries handled promptly
Our team is on hand to clarify anomalies or obtain missing information, ensuring smooth finalisation of returns without burdening your internal staff.
Deadline monitoring and reminders
We support your practice in tracking deadlines to avoid penalties, particularly useful during peak Self Assessment season.
Why MTD for ITSA changes everything
If Self Assessment season feels intense now, MTD for ITSA is about to add more pressure.
From April 2026, most landlords and self-employed clients earning over £50,000 will need to submit quarterly updates, plus the final year-end return, that’s five submissions per client, every year. In other words, you’re facing four extra deadlines per client, every single year, on top of the work you’re already doing.
And it doesn’t stop there:
No slow season
You’ll be preparing and submitting returns in April, July, October, January, and again at year-end.
Less time for advisory work
With the admin burden exploding, your higher-value services risk taking a back seat.
Digital record-keeping compliance
Every figure must come from MTD-compatible software, leaving zero room for manual workarounds.
More client chasing
You’ll need income and expense data four times as often, which means four times the emails, calls, and reminders.
For many firms, this shift will add more Self Assessment workload overnight. Outsourcing now gives you a ready-made, experienced tax team that can absorb the extra work, so you can handle MTD for ITSA without hiring more staff or burning out your current team.
Need help managing high volumes of Self Assessment returns?
We offer fast, accurate, and reliable support.
Accounting software used by us
Why choose Affinity Outsourcing for Self Assessment tax work?
Specialised expertise in Self Assessment compliance
Our team has in-depth knowledge of HMRC Self Assessment requirements, including complex cases involving multiple income streams, capital gains, and property income.
Peak season support you can rely on
We scale our resources during tax season to manage high volumes of Self Assessment returns without compromising accuracy or turnaround times.
Dedicated accounting partner
You’ll work with a consistent team that understands your clients, your systems, and your way of working, ensuring continuity and trust.
Accurate handling of tax reliefs and allowances
We are thorough in identifying all applicable reliefs, such as Marriage Allowance, SEIS, EIS, and pension contributions, to help your clients reduce their tax liabilities.
Secure and Compliant Data Management
We follow strict GDPR protocols and use encrypted portals for all document exchange and communication, ensuring your clients’ data is always protected.
Proactive error reduction and risk mitigation
Each return undergoes a multi-level review process, significantly lowering the chances of HMRC enquiries or late filing penalties.
What our clients say about us
McKenzie Philips Tax Accountants
Kevin Alderton & Team
The contrast with the previous outsourcing company could not have been clearer. Affinity provided us with a dedicated team in the UK and a team leader in India. We have an established system which allows us to prioritise our jobs making sure client satisfaction remains high. We like the ability to switch our usage on and off according to our work volumes and our capacity. Using Affinity Outsourcing has given us a significant competitive advantage and we continue to exploit this and increase our client numbers without compromising service levels.
Artisan Accountants
Using Affinity Outsourcing has changed both my business and my lifestyle. I have an amazing work life balance and knowing that I have a back up plan if there is a reason why I can’t work has helped me enormously. The added value is that I have managed to increase my GRF and therefore the capital value of the business for my retirement without any stress. I cannot recommend this way of working highly enough.
Ready to lighten your Self Assessment workload?
Get in touch today to discuss how our Self Assessment outsourcing can support your firm this tax season.
Frequently Asked Questions
1. Can you handle a large volume of Self Assessments during the January peak?
Yes. Our team is structured to handle bulk SA100 returns efficiently, with capacity scaling during the Self Assessment rush.
2. How early should I outsource Self Assessment work?
We recommend starting as early as July–August to avoid last-minute HMRC penalties and ensure a thorough review.
3. Do you deal directly with HMRC for Self Assessment issues?
Yes, we can respond to HMRC queries, update information, or negotiate payment plans—on your behalf.
4. How does outsourcing self-assessment save money for my firm?
You avoid hiring seasonal staff and reduce overtime hours for your team. Our efficient process means quicker turnaround and reduced cost per return.