The Quiet Margin: Pricing Platform Cash Against Its Alternatives in 2026
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Cash has become a product line. For many UK investment platforms, the balance sitting between trades is not merely a settlement convenience but a source of economics: client money is swept to banking partners, interest is earned, and a portion is passed back to the client. The arrangement is not inherently improper. It is, however, frequently opaque. A headline platform fee of 0.25% or 0.45% can tell an investor very little about the true cost of holding cash on the same platform, because the fee is only one of two margins at work. The second is the spread between what the platform earns on swept balances and what it pays to the client.
How the sweep economics actually work
In a typical sweep arrangement, uninvested client cash is placed with one or more banks under a client money or trust structure. The bank pays interest to the platform or its nominee, and the platform decides how much of that interest to retain and how much to pass through. Some platforms disclose a single rate; others use tiers, promotional rates or different rates for different wrappers. A few charge an explicit platform fee on cash balances as well as retaining interest, which can make the all-in cost harder to see.
None of this is necessarily unfair. Platforms provide custody, settlement, reporting and sometimes a banking-like service, and those functions have a cost. The editorial question is not whether a margin exists, but whether the client can identify it and compare it with genuine alternatives. Where disclosure is vague, the burden of diagnosis falls on the investor.
Why the headline fee understates the cost
Consider an illustrative platform with a 0.35% annual platform charge. If the platform pays 1.50% on cash while a comparable notice account pays 4.00%, the client is giving up 2.50 percentage points of gross yield before the platform fee is deducted. If the platform also applies its 0.35% charge to the cash balance, the net cash yield is approximately 1.15%, against 4.00% from the alternative. The headline fee has captured only a fraction of the economic difference.
That gap matters most when cash balances are large or held for long periods. It matters less for small, short-term settlement balances where access and integration have real value. The error is to treat a platform's cash rate as a default rather than a priced choice.
A five-test net-yield framework
First, establish the benchmark. Compare the platform rate with the prevailing Bank Rate, a short-dated gilt or money market fund yield, and a comparable notice account from a bank. Use the same tax wrapper and the same access terms.
Second, deduct every platform charge that applies to cash. Check whether the ad valorem fee is charged on cash as well as investments, whether there is a minimum monthly charge, and whether transfer or withdrawal fees apply. A rate quoted before platform charges is not a net yield.
Third, adjust for notice and access. A platform cash rate available on instant access is not directly comparable with a 90-day notice account. Assign a value to liquidity, but do so explicitly rather than allowing convenience to obscure the yield difference.
Fourth, examine protection and counterparty treatment. FSCS protection for swept cash depends on the structure: eligible deposits held with a bank are generally protected up to £85,000 per eligible depositor per banking licence, but platform failure and client money arrangements raise separate questions. Investors should understand whether they are relying on deposit protection, client money rules, or both.
Fifth, account for tax. Cash interest outside an ISA or SIPP may be subject to income tax and the personal savings allowance. A higher gross rate in a taxable account can produce a lower after-tax return than a sheltered rate inside an ISA.
The 2026 Consumer Duty lens
Consumer Duty has shifted the regulatory emphasis from disclosure alone to outcomes: price and value, consumer understanding, and the fair treatment of customers. Cash balances sit uncomfortably across those outcomes because the product is simple, the economics are not, and the client may not regard cash as a product at all. Firms are expected to assess whether retained interest and cash charges represent fair value, and to communicate clearly enough that clients can make an informed choice.
That does not mean every platform must pay the highest market rate. It does mean the basis for the rate should be intelligible, the charges should be visible, and the client should not have to reverse-engineer a revenue model to understand what they are earning. In 2026, the practical test is whether a reasonably informed investor can answer a simple question: what is my net cash yield, after all platform charges, and what am I giving up by holding cash here rather than elsewhere?
What advisers and DIY investors should do
Treat platform cash as a distinct allocation with its own yield, liquidity and protection profile. Review it at least annually, and more often when rates move. Ask for the gross rate, the platform charge applied to cash, the retention basis, the banking counterparties and the FSCS position. Compare the net figure with a notice account and a money market fund on a like-for-like basis. Where the platform cannot provide a clear answer, treat that opacity as a cost in itself.
The sweep is not free, but it is not automatically poor value either. The disciplined approach is to price it. Once the margin is visible, the decision becomes what it should be: a comparison of net yield, access and protection, rather than an accident of where the cash happens to sit.
