Basis Period Reform for Law Firms: Complete Guide for Partners and Practice Managers

Basis period reform is one of the most significant tax changes for legal partnerships in years. From the 2024/25 tax year, the way law firm partnerships and LLPs align their accounting periods with the tax year has changed, affecting how partners report and pay tax on their shares of practice profits. The 2023/24 tax year was the transition year that bridged the old rules and the new.

This reform touches every type of legal practice structure, from two-partner high street firms to large commercial LLPs. The changes are not optional. They apply automatically to all unincorporated businesses, with the tax-year basis in force from 2024/25 onwards.

What Is Basis Period Reform?

Basis period reform changes how partnerships align their accounting periods with the tax year for reporting purposes. Under the old rules, a partnership could draw up accounts to any date, and partners were taxed on the profits of the accounting period ending in the tax year (the "current year basis", which in practice often taxed profits earned well before the tax year in question).

From 2024/25 onwards, partners are taxed on the profits that actually arise in the tax year (6 April to 5 April), regardless of the accounting period end date. This is the "tax-year basis". Where a firm's accounts do not run to 31 March or 5 April, the year's taxable profit is built by apportioning two sets of accounts to cover the tax year.

For a Manchester law firm with a 30 April year end, the change works like this:

• 2022/23 and earlier: partners taxed on the accounting period ending in the tax year (for 2022/23, the year ended 30 April 2022)
• 2023/24: the transition year, in which the catch-up to 5 April 2024 is brought into account (see below)
• 2024/25 onwards: partners taxed on profits apportioned to the tax year 6 April to 5 April (the tax-year basis)

The 2023/24 Transition Year

The 2023/24 tax year was the transition year, the point at which firms caught up the gap between their old accounting date and 5 April 2024. Partners with a year end other than 31 March or 5 April can be assessed on more than 12 months of profit in the transition, which is the source of the cash flow pressure this reform creates.

Firms whose accounts already run to a date between 31 March and 5 April were largely unaffected, because their accounting period already lines up with the tax year. Firms with other year-end dates faced a transition calculation and, often, an additional one-off charge.

Example: Law Firm with a 31 December Year End

Consider a Birmingham partnership with three equity partners and a 31 December accounting date. Its transition year (2023/24) is built from two parts:

• the "standard part": the 12 months of the accounting period ending in 2023/24 (the year ended 31 December 2023)
• the "transition part": the catch-up period from 1 January 2024 to 5 April 2024, which closes the gap to the end of the tax year

The transition part, reduced by any unused overlap relief, is the firm's transition profit. Without overlap relief to absorb it, each partner faces an extra slice of taxable profit on top of a full year, which is why planning matters for firms with year ends well away from April.

Overlap Relief and Its Impact

The reform allows overlap relief to be set against the catch-up, which prevents permanent double taxation. When a partnership first started, partners built up "overlap profits", income that was taxed twice in the opening years because the early accounting periods overlapped. That overlap relief had to be used by the time of the transition.

In the 2023/24 transition year, overlap relief is deducted from the catch-up profit before the transition charge is worked out. The catch is that many established partnerships have little overlap relief available, particularly those that started many years ago when profits were lower, so the relief rarely covers the whole catch-up.

Partners who joined an existing practice rather than starting a new one typically have no overlap relief of their own, because overlap profits arise on commencement. For them, the catch-up profit can be fully exposed in the transition.

Spreading the Transition Profit

To soften the cash flow impact, the transition profit (the catch-up to 5 April 2024, net of overlap relief) is spread automatically over five tax years, from 2023/24 to 2027/28. By default a minimum of 20% is taxed each year, so a partner carries an additional slice of taxable profit annually until 2027/28.

A firm or partner can elect to bring the transition profit into charge faster than the default 20% a year, for example to use up a lower tax band in a particular year, or where a partner is approaching retirement. The transition profit is also treated separately for some purposes, which can help keep a partner's other income clear of higher thresholds. Whether to accelerate is a year-by-year modelling decision rather than a default.

Cash Flow Planning for Law Firms

The practical challenge is managing the cash flow effect of the transition. A partner may owe tax on more than 12 months of profit across the transition and the spreading years, while the practice's actual cash generation continues at its normal level. Lock-up (unbilled work in progress plus outstanding debtors) ties up the very cash partners need to meet those bills.

Key Planning Steps

• Quantify the transition profit: work out the catch-up to 5 April 2024 and deduct each partner's available overlap relief.
• Confirm overlap relief figures: trace historical overlap relief for each partner, as records can be incomplete for long-standing firms.
• Decide on the spreading profile: model the default 20% a year against electing to accelerate, partner by partner.
• Plan drawings and reduce lock-up: align drawings with the phased tax charge and tighten billing and collections to free up cash. See our guide on reducing law firm lock-up.

Different Practice Structures

Traditional Partnerships

In a traditional partnership the rules apply to each partner's profit share. Partners with different profit-sharing ratios, or those joining or leaving around the transition, may need individual transition and spreading calculations rather than a single firm-wide figure.

LLPs (Limited Liability Partnerships)

LLP members are taxed as self-employed partners on their profit share, so the tax-year basis and the transition rules apply to them in the same way as to a traditional partnership. LLP profit allocation agreements may need reviewing so they do not produce unintended results across the transition. For the wider picture, see how LLP members are taxed.

Sole Practitioners

Sole practitioner solicitors are also within basis period reform, since it applies to all unincorporated businesses. In practice many sole practitioners already drew accounts to 31 March or 5 April and so saw little change, but those with another year end faced the same transition and spreading. If a sole practitioner takes on a partner, the new partnership applies the tax-year basis from the outset.

WIP, Lock-up and the Cash Basis

Law firms recognise work in progress as revenue under FRS 102, so unbilled time sits on the balance sheet as an asset and is taxed as it is recognised, not simply when it is billed. That makes WIP a tax timing issue as well as a working-capital one, and it interacts with the transition because the profit being apportioned is accruals-based profit.

From 6 April 2024 the cash basis became the default for unincorporated businesses, but LLPs and partnerships with a corporate partner are excluded from it. In practice most law firms therefore continue to prepare accounts on the accruals basis, with WIP and debtors brought into account in the normal way. Reducing lock-up (WIP days plus debtor days) remains the core working-capital lever, and it is doubly important while the spreading charge runs.

Compliance and Record-Keeping

Firms should make sure their accounting systems can support the tax-year basis. That includes:

• maintaining detailed monthly profit and loss records, so two sets of accounts can be apportioned to a tax year cleanly
• tracking partner profit shares across the transition and spreading years
• preserving overlap relief records for each partner, which the transition relies on
• keeping tax compliance aligned with SRA Accounts Rules compliance, which governs client money separately from the firm's own tax position

Making Tax Digital Considerations

Making Tax Digital for Income Tax is being phased in for sole traders and landlords from April 2026 by income level, with partnerships brought in at a later date to be confirmed. Where it applies, partners will keep digital records and send quarterly updates, which sits alongside the tax-year basis already in force.

Practices should check whether their current software can handle both the apportionment the tax-year basis requires and the digital record-keeping that Making Tax Digital will bring. Our guide on Making Tax Digital for solicitors covers the timeline in more detail.

Getting Professional Help

The transition calculation, the interaction with overlap relief, and the choice over spreading mean most firms benefit from specialist input. Each partner's overlap relief, profit-sharing ratio and personal tax position is different, so the right answer on accelerating or spreading varies from one partner to the next.

A specialist accountant for solicitors can quantify the impact on each partner, model the spreading profile, and align it with drawings and lock-up reduction so the cash is there to meet the phased charge.

The stakes are real: getting the transition wrong can mean overpaying, underpaying, or missing a chance to use the spreading rules efficiently. For firms with a non-April year end and limited overlap relief, this is worth getting right well before each filing deadline.