Best Investment Platform UK: Stocks and Shares ISAs Compared by Cost

There is no single best investment platform in the UK, and anyone who tells you otherwise is usually being paid to. The right platform depends almost entirely on how much you have invested and how you invest, because platforms charge in two very different ways: a percentage of your pot, or a flat fee. For a small portfolio, percentage pricing is cheaper. For a large one, a flat fee wins by a wide margin. This guide compares the main UK platforms on total cost and matches each to the investor it genuinely suits, so you pay the least for what you actually do.

We keep this calm and cost-led, the way we keep everything on Rational GB. Fees are the one part of investing you can control with certainty, and over decades they matter more than most people believe. Before you compare providers, it is worth understanding exactly what you are paying, which we cover in fund fees and the OCF explained.

Why fees decide this, not features

Platform marketing loves apps, dashboards and research tools. Over a 20-year horizon, almost none of that moves your returns. Cost does. A difference of just 0.3% a year on a £100,000 portfolio can add up to more than £20,000 in lost growth over two decades, because you lose the fee and all the future growth that fee would have earned. So the sensible question is not “which platform has the nicest app”, it is “which platform costs me the least for the way I invest”.

Two numbers make up most of the cost: the platform fee (what the provider charges to hold your investments) and the dealing or transaction fee (what you pay to buy and sell). A percentage platform fee is cheap when your pot is small and gets expensive as it grows. A flat monthly fee is the opposite: painful on a small pot, excellent on a large one. Find where your portfolio sits on that line and the decision mostly makes itself.

The main UK platforms, by how they charge

Fees change, so treat the figures below as the current shape of each platform rather than a permanent quote, and check the provider’s own fee page before you open an account.

• Trading 212 charges no platform fee and no dealing fee on its stocks and shares ISA, which makes it the cheapest headline option for many DIY investors. It earns money elsewhere, including a small currency conversion charge on foreign shares, so it suits people buying UK-listed or low-cost global ETFs. See our Trading 212 review for the detail.
• InvestEngine charges no account fee for DIY investors who build their own portfolio from ETFs, with a small charge only on its managed option. It is a strong pick if you want a clean, ETF-only ISA without a platform fee. Our InvestEngine review covers the trade-offs.
• Vanguard charges around 0.15% a year, capped at £375, but you can only hold Vanguard’s own funds. For someone who wants a simple, low-cost, one-provider ISA built around a fund like LifeStrategy, it remains a sensible default. We look at that fund in the Vanguard LifeStrategy review.
• AJ Bell charges a percentage platform fee but caps the charge on shares and ETFs, which makes it good value for a broad-choice ISA once your pot grows. It suits investors who want a wide universe of funds, shares and investment trusts.
• Hargreaves Lansdown is the largest and most feature-rich, but its fund platform fee is among the highest, so on pure cost it is hard to justify for a new ISA unless you specifically value its service and research.
• Interactive Investor charges a flat monthly fee rather than a percentage. That is poor value on a small pot but excellent once your portfolio is large enough that the flat fee undercuts a percentage charge.

Which platform for your portfolio size

The clean way to choose is by pot size.

Starting out, under about £25,000. A zero-platform-fee provider like Trading 212 or InvestEngine, or Vanguard’s capped percentage, will almost always be cheapest. Avoid flat-fee platforms at this stage; the monthly charge eats a meaningful slice of a small pot.

Growing, roughly £25,000 to £80,000. This is the crossover zone. Percentage platforms are still fine, but keep an eye on the total. If you want broad choice, AJ Bell’s capped share and ETF pricing starts to look attractive here.

Larger, above roughly £80,000 to £100,000. A flat-fee platform such as Interactive Investor usually becomes the cheapest option, because a fixed monthly charge stops growing while a percentage fee keeps climbing with your pot. The larger your portfolio, the more a flat fee saves you.

These bands are guides, not hard lines, and the exact crossover depends on whether you hold funds or shares and how often you trade. Run your own pot through a fee comparison before you commit; we go deeper on this in the cheapest stocks and shares ISA platform comparison.

Before you pick: the account, then the platform

One thing people get backwards: decide the account type first, then the platform. Most long-term investors want a stocks and shares ISA, because gains and income inside it are tax-free up to the annual ISA allowance, which you can confirm on the government-backed MoneyHelper site. If you are investing for retirement specifically, a SIPP may suit you better for the tax relief. Only once you know the wrapper do the platform fees become comparable like for like.

If you are at the very start, read how to start investing in the UK first, then come back here to choose where to hold it. And whatever platform you land on, keep the investments inside it simple and low-cost; our best index funds UK guide is the natural next step.

Frequently asked questions

What is the best investment platform in the UK? It depends on your portfolio size. For smaller pots, a zero-platform-fee provider like Trading 212 or InvestEngine, or Vanguard’s capped percentage fee, is usually cheapest. For larger pots above roughly £80,000 to £100,000, a flat-fee platform such as Interactive Investor tends to cost the least. Match the fee structure to your pot.

Is a percentage fee or a flat fee cheaper? A percentage fee is cheaper on a small portfolio and gets more expensive as your pot grows. A flat fee is expensive on a small pot but excellent on a large one, because it stops rising while a percentage charge keeps climbing. The crossover is usually somewhere around £80,000 to £100,000.

Does the investment platform affect my returns? Yes, through cost. Platforms do not change how your funds perform, but their fees come straight out of your returns every year. A difference of even 0.3% a year compounds into tens of thousands of pounds over decades on a large portfolio, so choosing a low-cost platform is one of the few reliable ways to keep more of your growth.

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-free status, as long as you use the provider’s official ISA transfer process rather than withdrawing the cash yourself. Many people start on a low-fee platform and move to a flat-fee one as their pot grows.

Is Trading 212 really free? Its ISA has no platform fee and no dealing fee, which is genuinely cheap, but no platform is free to run. Trading 212 makes money in other ways, including a small currency conversion charge when you buy foreign shares. For a DIY investor holding UK-listed or global ETFs, it remains one of the lowest-cost options.