Open your last ISA statement and look for the line marked "platform fee" or "service charge". Most people skim straight past it on the way to checking whether their tracker fund is up this month, and that habit is exactly what costs them money. A difference of 0.3 percentage points in annual charges looks trivial on paper, but compounded over fifteen years on a £60,000 portfolio it can add up to several thousand pounds — enough for a decent kitchen, or a chunk of a deposit. Nobody sends you a letter pointing this out, because the platform charging you the fee has no incentive to make you think about it.
Here's the uncomfortable part: the platform you opened your ISA or SIPP with five or ten years ago is very unlikely to be the cheapest option for you today. Fee structures have shifted, new entrants have undercut the old guard, and most investors never revisit the decision once the account is open. Switching provider sounds like admin nobody wants, but for a lot of people it's the single highest-value hour they'll spend on their finances this year.
The fee you don't see is still coming out of your return
Platform charges come out automatically, usually monthly or quarterly, straight from your cash balance or by selling down a sliver of your holdings. You never sign anything to authorise it and you rarely get an email drawing attention to it, which is precisely why it's so easy to ignore. Add up a 0.45% platform fee, a fund's own ongoing charges figure of maybe 0.22%, and possibly a dealing fee every time you buy, and you can be losing close to 1% a year before your investments have done anything at all. Over a working lifetime of saving into a pension, that's not a rounding error. It's the difference between a comfortable retirement and a tight one. And because HMRC's £20,000 annual ISA allowance and pension tax relief already do a lot of the heavy lifting for you, letting a platform quietly claw back a chunk of that advantage through fees is a genuinely avoidable waste.
How the big platforms actually charge you
UK platforms fall into roughly three pricing models, and knowing which one you're on matters more than knowing the headline number.
Percentage-based: Hargreaves Lansdown and AJ Bell
Hargreaves Lansdown charges a tiered annual platform fee of around 0.45% on funds, dropping as your holdings grow past £250,000, plus a separate charge capped at £45 a year for shares, ETFs, and investment trusts held in an ISA. That cap is the crucial detail — it means HL becomes relatively cheap for a shares-only ISA once your pot passes roughly £10,000, because the percentage stops mattering. AJ Bell runs a similar model but undercuts HL on the headline rate: 0.25% on funds, and a shares fee capped at £3.50 a month rather than an annual figure. For a mixed portfolio of funds and individual shares, AJ Bell is usually the cheaper of the two, and I'd say it's the better default unless you specifically want HL's research tools or its customer service reputation, which is genuinely strong.
Flat fee: interactive investor
interactive investor takes a different approach entirely — a fixed monthly subscription, roughly £4.99 to £11.99 depending on the plan, rather than a percentage of your assets. That structure inverts the maths completely. If you're sitting on £150,000 or more, a flat £71.88 a year (the Investor plan billed annually) will beat almost any percentage-based competitor, because a 0.25% fee on that pot would already cost you £375. If you're starting out with £5,000, the same flat fee is punishingly expensive relative to your balance. This is the single most common mistake I see people make when choosing a platform: they pick based on brand recognition rather than doing the arithmetic for their own pot size.
Low-cost and zero-commission: Vanguard Investor, Freetrade, Trading 212
Vanguard's own platform, Vanguard Investor, charges a 0.15% account fee capped at £375 a year, which is hard to beat if you're happy holding mostly Vanguard funds and trackers, though it's noticeably less flexible if you want a wide universe of individual shares or investment trusts. Freetrade and Trading 212 sit at the other extreme: no platform fee at all on their basic tiers, and no dealing commission on trades. Trading 212 offers a genuinely fee-free ISA; Freetrade charges a modest monthly fee, around £4.99, for ISA access on its Standard plan, though its most basic General Investment Account tier remains free. These apps aren't for everyone — the research and reporting tools are thinner than HL or AJ Bell — but for a straightforward buy-and-hold ETF portfolio, they're difficult to argue against on cost alone. If you're just starting out with a few thousand pounds and no interest in individual share picking, choose one of these over Hargreaves Lansdown — a percentage fee on a small balance does disproportionate damage, and there's no research subscription worth paying for at that stage.
Dealing fees change the answer again
Platform fees get most of the attention, but dealing charges quietly decide the winner for anyone who trades individual shares rather than just holding funds. Hargreaves Lansdown charges around £11.95 for an online UK share deal, dropping to £5.95 if you've placed ten or more deals in the previous month. AJ Bell charges roughly £9.95, falling to £4.95 for frequent traders on the same sliding scale. Both firms also run regular investing plans — buying on a fixed day each month — for around £1.50 a trade, which is a far cheaper way to build a share portfolio gradually than dealing ad hoc at the standard rate. Trading 212 and Freetrade skip this calculation entirely by charging nothing for the trade itself, which is precisely why they win outright for anyone doing frequent small purchases into ETFs.
Why the "best" platform depends on the size of your pot, not the brand
There isn't a single winner here, and any comparison site that tells you otherwise is oversimplifying. The right way to think about it is: work out your likely portfolio size in twelve months, decide roughly what mix of funds versus individual shares you'll hold, and then run the actual numbers for two or three candidate platforms using their published fee calculators. A £20,000 ISA invested entirely in low-cost index funds will usually do best on a percentage-fee platform with no dealing charges, because the percentage itself stays small. The same £20,000 spread across fifteen individual shares, rebalanced a few times a year, tells a completely different story once dealing fees are added in. Someone with £40,000 across a handful of funds and a dozen shares, adding £300 a month, sits right at the point where flat-fee and percentage-fee models cross over — that's exactly the profile where it's worth running ii's fee calculator against AJ Bell's rather than assuming either one wins by default.
SIPPs charge differently, and the gap between providers can be bigger
Pension platform fees deserve separate attention because the caps and tiers often differ from the equivalent ISA on the same platform. Hargreaves Lansdown's SIPP carries the same 0.45% tiered fund charge as its ISA, but the shares fee cap is higher, around £200 a year rather than £45, reflecting the fact that pensions tend to hold larger balances over a longer horizon. AJ Bell's SIPP follows the same 0.25%/£3.50-a-month structure as its ISA, which keeps it competitive at almost any pot size. interactive investor bundles SIPP access into its standard monthly plans rather than charging separately, which again favours larger, longer-held pensions over small, newly-opened ones. The bit that catches people out: SIPP withdrawal and drawdown fees are a separate line item from the platform charge, and they vary far more between providers than the headline platform fee does. Check them before you commit, not after you've already built up fifteen years of contributions with one provider.
Switching platforms is less painful than it looks
The mechanism for moving an ISA or SIPP is called an "in-specie transfer" if you want to keep your existing holdings intact, or a cash transfer if you're happy to sell everything and rebuy on the new platform. In-specie transfers preserve your investments exactly as they are and avoid triggering any capital gains tax event, but they typically take four to eight weeks, and some funds simply aren't available on every platform, forcing a partial cash conversion regardless. Cash transfers are faster, often two to three weeks, but you're out of the market for that window, and for a SIPP or ISA that's a real, if usually small, risk rather than a purely administrative one.
Most receiving platforms will handle the paperwork for you once you fill in a transfer form on their website; you don't need to contact your old provider directly, and you should never withdraw the money yourself and try to move it manually, because that resets your ISA allowance rules for the year and can create an unwanted tax event on a pension. Some platforms, HL and AJ Bell among them, have occasionally offered cashback for transferring in a large ISA or SIPP, and it's worth checking current offers before you initiate anything, since a £200 or £300 cashback payment can make an otherwise marginal switch clearly worthwhile.
When staying put is the right call
None of this means you should chase the cheapest platform on the market every time a new one launches. If you're within a year or two of drawing down a SIPP, the disruption of a transfer — even a smooth in-specie one — probably isn't worth the saving, especially if your current platform's exit fees eat into it. And if you hold legacy investments that aren't available on cheaper platforms, forcing a sale to switch can trigger capital gains tax outside a tax wrapper, or simply mean rebuying at a worse price than you sold at. Do the sums for your specific pot before you move anything, not after you've already submitted the transfer form.