Basis Period Reform: Avoid the 2025 Summer Tax Shock
Aug 23, 2025
Why Everyone’s Talking About This in 2025
This summer, many sole traders in the UK are opening HMRC statements and seeing bigger-than-expected tax bills. The reason? Basis Period Reform is no longer just a policy change – it’s now impacting real payments.
For accountants, this isn’t just another tax update. It’s a chance to step up, support clients through unexpected liabilities, and build trust through smart planning.
What Changed and Why It Matters Now
Until recently, sole traders were taxed based on their accounting year-end (for example, profits to 30 April). But from 2024–25, everyone is taxed on profits earned during the actual tax year (6 April–5 April).
To move to this new system, HMRC introduced a “transition year” in 2023–24. This means some businesses are now being taxed on more than 12 months of profit – and the extra part is called transitional profit.
Even though these profits can be spread over 5 years, the higher tax bills start now, and many clients are completely unprepared.
A Simple Example
Let’s say your client Lucy runs a business with a 30 April year-end.
- For 2022–23, she was taxed on 12 months of profit: £60,000.
- In 2023–24 (the transition year), HMRC taxes her on 23 months of income:
- Normal 12 months = £60,000
- Additional 11 months (May 2023–March 2024) = £55,000
- Total taxable: £115,000
Lucy can choose to spread that extra £55,000 over 5 years. That adds £11,000/year to her taxable income – starting now.
Even with spreading, her tax bill rises, and her payments on account in 2025 are higher. Without planning, she could face cashflow issues.
Why This Summer is Critical
Clients are noticing the impact now because:
- The first instalments on transitional profits are due
- Payments on account for 2024–25 are based on higher income
- Many didn’t understand this change or forgot it was coming
If your firm doesn’t proactively explain and help plan, clients might:
- Feel blindsided
- Underpay HMRC and get hit with interest
- Lose confidence in your support
How You Can Help Clients Right Now
Here’s how top firms are handling it:
- Forecast Cashflow with Clients – Use real data to show what their payments will look like in 2025 and beyond. Help them understand what they owe and when.
- Explain Spreading Options Clearly – Most will choose the 5-year spread, but some might benefit from paying sooner. Tailor it based on each client’s income outlook.
- Adjust Payments on Account – Recalculate payments so they’re realistic and don’t lead to underpayment penalties.
- Proactive Conversations – Don’t wait until January. This summer is the right time to reach out, educate, and guide your clients before it’s too late.
Turning Advice into Opportunity
Many firms are turning this into a simple paid advisory service. You can offer:
- Fixed-fee tax impact reviews
- Transition planning sessions
- Add-on support for cashflow forecasting
Clients appreciate clarity, especially when it prevents a financial shock. And it’s a great way to build trust and value.
SandMartin Can Support You
Need help delivering this at scale?
At SandMartin, we support UK accounting firms with offshore teams that handle:
- Transitional profit calculations
- Client letters and education packs
- Cashflow modelling support
- Admin and follow-ups
We act as an extension of your practice, giving you more capacity without sacrificing quality.
Final Thoughts
Basis Period Reform is no longer in the future – it’s affecting your clients now.
- Start the conversations this summer
- Help them model and spread their profits wisely
- Make tax planning a trusted part of your service
Don’t let a policy change turn into a client crisis. Let’s help them through it.