The Basel IV framework, implemented in the UK through the PRA's near-final rules under what the PRA has labelled the Basel 3.1 standards, represents the most significant revision to bank capital calculation methodology in over a decade. The PRA published near-final rules in September 2024, with a phased implementation timeline that starts in January 2027 for most components. That timetable looks distant until you account for the data, systems, and process changes that need to be in place before reporting under the new standards can begin.
This article covers the main areas compliance and finance teams need to track, based on the PRA's published rules and the Basel Committee's final standards where PRA has not yet diverged from them. It is not a substitute for reading the PRA's near-final rules in full. It is a checklist for ensuring the right work is underway.
The Output Floor: How It Works and When It Bites
The most discussed element of Basel IV is the output floor. The output floor limits the extent to which banks can reduce their risk-weighted assets (RWAs) by using internal models. Starting at 50 percent in year one of the phase-in, the floor rises to 72.5 percent of the standardised approach calculation by January 2030. At full implementation, a bank whose internal models produce an RWA calculation lower than 72.5 percent of what the standardised approach would produce must use the standardised approach figure instead.
For banks with well-calibrated internal models, the output floor may not bite immediately. For banks whose internal models have historically produced significant reductions to standardised RWAs (common in mortgage lending, where LTV-based standardised risk weights can be conservative relative to modelled experience), the floor creates material additional capital requirements that phase in over the transition period. Finance teams that have not yet modelled the year-by-year capital impact of the output floor ramp-up across their portfolio mix are working with incomplete planning assumptions.
Revised Standardised Approach: Credit Risk
The standardised approach for credit risk is being revised as part of Basel IV, and the changes affect the risk weights applied to key exposure categories. The most significant change for most retail and commercial banks is the revised treatment of real estate exposures. Under Basel IV, residential real estate risk weights are differentiated by loan-to-value ratio at a more granular level than under current rules, with risk weights ranging from 20 percent for exposures secured on property where the LTV is below 50 percent, up to 70 percent for LTVs above 80 percent at the time of origination.
The treatment distinguishes between exposures that are materially dependent on cash flows from the property (income-producing real estate) and those that are not. Income-producing real estate exposures attract higher risk weights under the revised standardised approach. Compliance teams working on Basel IV implementation need to confirm that the origination-LTV data required to apply these risk weights is captured and accessible for reporting purposes. For portfolios with legacy origination data, confirming data quality across older tranches is a practical prerequisite.
Market Risk: FRTB and What It Requires
The Fundamental Review of the Trading Book (FRTB) is the Basel IV component with the most operational complexity for banks with trading book activity. FRTB replaces the current internal models approach (IMA) for market risk with a stricter approval process and introduces the sensitivities-based standardised approach (SSA) as the floor and alternative where IMA approval is not obtained.
Under FRTB, banks must clearly assign positions to either the trading book or banking book, with strict criteria governing the assignment and limited ability to reassign. The internal models approach under FRTB requires desk-level regulatory approval, including a P&L attribution test that checks whether the risk model's theoretical P&L aligns with the actual P&L generated by the trading desk. Banks that cannot pass the P&L attribution test for a given desk must use the standardised approach for that desk, even if they have IMA approval for others. For compliance teams, FRTB introduces reporting and governance requirements around trading book boundary policies and desk-level model approval status that are different in character from current market risk reporting.
Operational Risk: The Standardised Measurement Approach
Basel IV replaces the multiple existing approaches to operational risk capital calculation (Basic Indicator Approach, Standardised Approach, Advanced Measurement Approach) with a single Standardised Measurement Approach (SMA). The SMA calculates operational risk capital as a function of the bank's Business Indicator Component (BIC) and its Internal Loss Multiplier (ILM), which incorporates the bank's 10-year history of operational losses.
The ILM creates a direct capital charge impact from historical loss events. A bank with a material operational loss in its 10-year window will carry a higher SMA capital requirement than one without, all else equal. This creates a long-tail compliance consideration: operational loss events recorded today will remain in the SMA calculation for a decade. The incentive to invest in operational risk controls is now more directly connected to capital requirements than under previous approaches.
We are not saying the SMA is simpler than the Advanced Measurement Approach it replaces. The data requirements, particularly the 10-year operational loss history with the categorisation required for SMA purposes, are significant. Banks moving from AMA to SMA need to confirm the historical loss data they hold meets the SMA's requirements before the transition date.
The PRA Implementation Timeline: What to Track
The PRA's phased implementation starts 1 January 2027, with the output floor beginning at 50 percent and the full framework applying. The floor reaches 72.5 percent on 1 January 2030. The PRA is expected to publish additional technical standards and supervisory statements as the implementation date approaches, and these publications will refine requirements in areas where the near-final rules left discretion.
The compliance function's role in Basel IV implementation is different from the finance function's role, but they are interdependent. Finance owns the capital calculation methodology changes. Compliance owns ensuring that the required processes, data governance, and governance documentation (including the trading book boundary policy and any IMA model governance requirements) are in place and that the firm can demonstrate adherence to them under PRA review. The compliance checklist for Basel IV cannot be produced by the compliance function alone; it requires input from finance, risk, and technology on what the calculation methodology changes actually require.
Ongoing Monitoring: PRA Publications
The PRA is publishing technical standards and supervisory expectations on an ongoing basis as the January 2027 implementation date approaches. The near-final rules published in 2024 are not the last word. Areas where further clarification has been signalled include the credit risk mitigation framework under the revised standardised approach, the definition of eligible collateral for risk weight reduction purposes, and the interaction between the output floor and the leverage ratio.
Compliance teams that have delegated their Basel IV monitoring to finance and are not tracking PRA publications in this area will find gaps in their implementation tracking. Kalipso tags PRA publications by regulatory framework, including Basel 3.1 implementation, so compliance teams receive alerts when the PRA adds to its published guidance rather than relying on finance or external counsel to flag relevant publications. The gap between implementation deadline and the current date is shorter than it looks when you account for lead times on systems changes. Tracking ongoing PRA guidance is a necessary part of that preparation, not a nice-to-have.
