A stocks and shares ISA is a wrapper, not an investment. It sits around whatever you buy, index funds, ETFs, individual shares, and shelters the growth and income from UK tax. The investments do the work. The platform just holds them and charges you for the privilege.

Which means the single biggest decision most people get wrong is not what to buy. It is paying too much to hold it. Over a few years the gap between a cheap platform and an expensive one is small. Over twenty or thirty years it quietly eats a meaningful slice of your pot. So this guide leads with fees, names real numbers, and tells you which platform fits which size of portfolio.

All charges below were checked against each provider’s own fee pages in 2026. Several platforms repriced over the past year, so older comparison articles are out of date. We have flagged the changes where they matter.

How platform fees actually work

There are two charging models, and almost every platform uses one of them.

  • Percentage fee. You pay a slice of your holdings each year, typically 0.15% to 0.45%. Cheap when your pot is small, expensive once it grows. A 0.45% fee on £100,000 is £450 a year.
  • Flat fee. You pay a fixed monthly amount whatever your balance. Expensive when your pot is small, cheap once it is large. A £5.99 monthly fee is £71.88 a year on £5,000 or on £500,000.

On top of the platform fee you may pay dealing charges (a fee each time you buy or sell), an FX fee when you buy something priced in dollars or euros, and the fund’s own ongoing charge (the OCF), which goes to the fund manager, not the platform. A cheap platform holding an expensive fund is not a cheap arrangement.

The rule of thumb: small and growing pots usually win with a percentage platform; large pots usually win with a flat fee. The crossover sits somewhere around £30,000 to £80,000 depending on how you invest. We will be specific below.

The fee-first shortlist for 2026

Trading 212: cheapest for most starters

Trading 212 charges no platform fee and no dealing fee on its stocks and shares ISA. The only cost the broker can apply is a 0.15% FX fee when you buy an asset priced in another currency. For someone drip-feeding a global index ETF every month, the running cost is close to nothing beyond the fund’s own OCF.

The trade-off is that this is a leaner, app-led service rather than a full-service broker, and the investment range is shares and ETFs rather than unit trusts, OEICs or investment trusts. For a first ISA built around one or two index ETFs, that is rarely a problem.

InvestEngine: cheapest for ETF-only investors

InvestEngine charges £0 platform fee on its DIY ETF portfolios, with no setup, trading or withdrawal fees. You pay only the ETF’s own OCF. Hold a global tracker with a 0.22% OCF and your all-in cost is 0.22%, full stop. Its managed LifePlan portfolios add a 0.25% management fee on top of the ETF costs, which works out to roughly 0.45% all in once underlying charges and spreads are counted. That is the price of having someone else run it.

The catch is that InvestEngine is ETFs only. No individual shares, no unit trust funds. If a global ETF is your whole plan, that limitation costs you nothing.

Vanguard Investor: simple, but no longer the default cheap pick

Vanguard used to be the reflex answer for cheap index investing. It now applies a £4 a month minimum fee for balances below £32,000. At or above £32,000 you pay the 0.15% account fee, capped at £375 a year. Fund OCFs run from roughly 0.06% to 0.79% depending on what you hold.

That £4 monthly floor (£48 a year) matters for smaller pots. On a £3,000 ISA, £48 is 1.6% a year, which is steep for an index investor. The bigger constraint is that you can only buy Vanguard’s own funds, around 75 of them. If a Vanguard LifeStrategy or FTSE Global All Cap fund is exactly what you want, the platform is clean and predictable. If you want choice, look elsewhere.

AJ Bell: the value pick once your pot grows

AJ Bell repriced for 2026 and is now hard to beat for share, ETF and investment trust holdings. The custody charge on shares, ETFs and investment trusts in an ISA is 0.25% but capped at £3.50 a month, which is £42 a year, no matter how large the holding. Funds (unit trusts and OEICs) carry a tiered 0.25% charge. Share dealing is £5 a trade, dropping to £3.50 if you placed 10 or more share deals the previous month. Fund dealing is £1.50, and regular monthly investing becomes free from May 2026. The foreign exchange charge starts at 0.75% and tiers down on larger international deals.

For a £50,000 portfolio of ETFs and trusts, the £42 cap makes AJ Bell one of the cheapest mainstream homes in the country, with a full-featured platform behind it.

Hargreaves Lansdown: cheaper than it was, still premium

Hargreaves Lansdown is the largest UK platform and historically the most expensive. From 1 March 2026 it cut its main ISA platform fee from 0.45% to 0.35% on portfolios under £250,000, and raised the annual cap on shares, ETFs and investment trusts to £150 a year. Share dealing dropped to £6.95 (or £3.95 if you placed more than 20 trades the previous month), and it introduced a new £1.95 fund dealing fee that did not exist before. Regular monthly investing remains free of dealing charges.

The picture is mixed. Most ISA customers pay a little less than they did, but the new fund dealing fee and the higher share cap mean some are slightly worse off. HL still costs more than AJ Bell or Trading 212. You pay for the service depth, research and customer support, which some investors value and many do not need.

Interactive Investor: a flat fee for larger pots

Interactive Investor charges a flat monthly subscription rather than a percentage, which is what makes it compelling once your portfolio is large. From February 2026 its plans are Core at £5.99 a month (suited to portfolios up to £100,000), Plus at £14.99 a month, and Premium at £39.99 a month for frequent traders. FX is a flat 0.75% on Core, tiering down on the higher plans.

On a £150,000 portfolio, Plus at £14.99 a month is £179.88 a year. A 0.35% percentage fee on the same pot would be £525. The maths flips firmly in favour of flat fees as your balance climbs.

Freetrade: a free ISA for app-first investors

Freetrade’s free Basic plan now includes a stocks and shares ISA and a SIPP at no monthly cost, alongside commission-free trading. That makes it a genuine zero-fee option much like Trading 212, with the main running cost being a 0.99% FX fee on non-sterling trades. Pay £4.99 a month for the Standard plan and that FX fee falls to 0.59%; the Plus plan at £9.99 a month cuts it to 0.39% and adds a wider investment range. For someone who buys mostly UK-listed shares or ETFs and wants a simple app, the free tier is the obvious place to start.

Which platform fits which investor

Pick by how you invest and how big your pot is, not by the brand you have heard of.

  • First ISA, small and growing, buying index ETFs: Trading 212, InvestEngine or Freetrade’s free Basic plan. No platform fee means almost all your money stays invested.
  • You want Vanguard’s own funds and nothing else: Vanguard Investor, as long as your balance clears £32,000 so the £4 monthly floor is not biting.
  • £30,000 to £150,000 in ETFs and investment trusts: AJ Bell, where the £42 a year share cap is the standout.
  • £100,000-plus and value flat fees: Interactive Investor Plus, where a fixed £14.99 a month beats any percentage.
  • You want full research and service and accept paying for it: Hargreaves Lansdown, cheaper after the March 2026 cut but still premium.

If your priority is the lowest possible running cost across every pot size, our companion guide to the cheapest UK investment platforms runs the full fee table with worked examples at each balance.

Fees are not the only thing, but they are the first thing

A cheap platform with a fund range you cannot use is not cheap for you. Check that the platform offers the specific funds or ETFs you want, that the app or website is one you will actually use, and that it carries the account types you need now and later, an ISA today, perhaps a SIPP in a few years.

Two things you do not need to lose sleep over. Every platform named here is authorised by the Financial Conduct Authority and covered by the Financial Services Compensation Scheme up to £85,000 per person, per firm if the platform itself fails. That protection covers provider failure, not falls in the market value of your investments, which no scheme covers. You can confirm a firm’s status on the FCA register before you sign up.

The plain truth is that the right platform is the one that holds what you want to buy at the lowest cost you can find, then gets out of the way. Pick it once, keep your charges low, and let the time do the work.

Frequently asked questions

What is the cheapest stocks and shares ISA in the UK for 2026? For most starters buying index ETFs, Trading 212, InvestEngine and Freetrade’s free Basic plan are the cheapest, with no platform fee and no dealing charges. You pay only the fund’s own ongoing charge, plus a small FX fee if you buy assets priced in another currency. For larger ETF and investment trust portfolios, AJ Bell’s £42 a year share cap is hard to beat.

Is a percentage fee or a flat fee better? It depends on your pot size. A percentage fee (typically 0.15% to 0.45%) is cheaper when your balance is small and rises as your pot grows. A flat monthly fee stays the same whatever your balance, so it wins once your portfolio is large. The crossover point is usually somewhere between £30,000 and £80,000, depending on how you invest.

How much can I put in a stocks and shares ISA in 2026/27? The total ISA allowance for the 2026 to 2027 tax year is £20,000, shared across all your ISAs. You can split it between a cash ISA, a stocks and shares ISA, an innovative finance ISA and a lifetime ISA in any combination, as long as the total does not exceed £20,000.

Is my money safe in a stocks and shares ISA? Your investments are held separately from the platform’s own money, and the Financial Services Compensation Scheme covers up to £85,000 per person, per firm if an FCA-authorised provider fails. That protection does not cover losses if your investments fall in value, which is normal market risk that no scheme insures against.

Can I move my ISA to a cheaper platform later? Yes. You can transfer a stocks and shares ISA to another provider without losing its tax-sheltered status, and doing so does not use up your annual allowance. Some platforms charge an exit fee, though many have dropped these. Always request a formal transfer rather than withdrawing and re-depositing, which would waste your allowance.

Do I pay tax on a stocks and shares ISA? No. Growth, dividends and interest inside a stocks and shares ISA are free of UK income tax and capital gains tax, and you do not need to declare them on a tax return. That tax shelter is the whole point of the wrapper, which is why keeping the platform fee low matters so much: the savings compound untaxed.