What the Fat Cat Index measures

The Fat Cat Index  quantifies the gap between the most expensive investment platforms in the market versus a low-cost baseline (for this, we use the average cost of the five best-value providers). 

To show how high costs impact different types of investors, IG groups people into three activity profiles to reflect how trading frequency affects costs.

• Passive - 1 trade per month
• Medium - 3 trades per month
• Active - 6 trades per month

Across all types of investor, we applied a combination of HMRC data on average pot size and annual contributions, and IG customer data on geographical allocation, to calculate overpayment.

What does the 2026 Fat Cat Index tell us? 

Most UK investors are paying hundreds of pounds more than they need to in platform fees each year.

According to research undertaken as part of the Fat Cat Index, over half (52%) of UK investors are currently using the market's 12 most expensive Stocks and Shares ISA providers.

For an ‘active’ investor using a Stocks and Shares ISA with one of these platforms, the cumulative fees would be £515 more per year than if they used one of the market’s low-cost alternatives. For active investors using one of the four most expensive platforms, the average annual overpayment rises to £711, while for those using the most expensive firm, it’s £922.

For less active investors, the costs are still significant. The average ‘passive’ investor using one of the 12 higher-cost platforms would still pay £263 more per year than if they used one of the market’s low-cost alternatives, while for those making three trades per month, the figure is £357.

Table showing what different types of Stocks and Shares ISA investors are overpaying

Chart shows how much active, medium and passive investors overpay in Stocks and Shares ISA fees each year.

Which platforms cost the most for Stocks & Shares ISAs?

12 most expensive providers in IG’s Fat Cat Index based on ‘active’ investor profile (six trades per month)

Annual fees for this chart calculated using ‘active’ investor profile (6 trades per month). Price data accurate as of January 2026.

Fees and why they matter

Even relatively small differences in fees can have a compounding effect over time. For example, with active investors using one of the four most expensive platforms, the average annual overpayment is £711. Over a 40-year investing lifetime, this would amount to almost £28,440 in avoidable costs, based on today’s fees, and not accounting for lost compounding or an increase in annual contributions.

Different platforms charge fees in many different ways, which can make it confusing to know what you’re paying. Here are the types of fees investors can encounter on a stocks & shares ISA account:

• Annual administration fee
• Subscription fee
• Transaction/dealing fee
• FX fee
• Deposit and withdrawal fee

As a rule of thumb, the more charges you’re paying, the more likely you are to be overpaying.

What investors can do

• Check your fees: Compare what you’re paying to the baseline and see if you could save by switching. 
• Consider switching: Moving from a high-cost to a mid-tier provider can save hundreds per year. Try out IG’s new cost comparison tool to see what you could save by transferring your Stocks and Shares ISA to IG.
• Stay informed: Regularly reviewing your ISA costs helps ensure you’re not overpaying unnecessarily.

How we calculated overpayment

Overpayment is calculated as the difference between a platform’s Total Annual Cost (TAC) and the average TAC of the five lowest-cost providers (and yes, IG is one of them!).

TAC includes all the core costs an investor pays and can include:

• Annual platform fees
• Subscription fees
• Dealing fees based on trading frequency
• FX costs for international trades

Investor behaviour for the model is based on a combination of HMRC data and IG customers’ ISA portfolios. Fee structures, spreads and commission rates were sourced from provider websites and were correct as of 1st February 2026. You can see more detail on the methodology in our Notes section below.

All trading involves risk. 

The value of shares, ETFs and ETCs bought through a share dealing account, a Stocks and Shares ISA or a SIPP can fall as well as rise, which could mean getting back less than you originally put in. Past performance is no guarantee of future results. 

Notes

About the data

What is the IG Fat Cat Index?

The IG Fat Cat Index quantifies the gap between a provider’s Total Annual Cost (TAC) and a low-cost benchmark in the market. For the press release calculations, the low cost benchmark is the average TAC of the five lowest-cost providers in the shortlist of 25 major investment providers (based on the behaviour of an ‘active investor’, assuming 6 trades per month and a 40% allocation to international shares). The platforms in the low cost benchmark are Trading 212, Freetrade, XTB, IG and Revolut, with the benchmark sitting at £54.27 as of 1st February 2026.

How is Total Annual Cost calculated?

TAC is calculated using the following formulae. 

For a platform that charges a % for a dealing charge:

TAC = (Annual Platform Fee % × Average HMRC portfolio size) + Flat annual platform fee (if any) + (total value traded per year [which = annual subscriptions plus portfolio turnover] × Dealing Fee % charge) + ( total value traded per year  × Proportion executed in FX × FX Spread)

For a platform that charges a £ dealing fee, not a percentage:

TAC = (Annual Platform Fee % × Average HMRC portfolio size) + Flat annual platform fee (if any) + (72 × Dealing Fee £ charge) + ( total value traded per year   × Proportion executed in FX × FX Spread)

Fee structures, spreads and commission rates were sourced from provider websites and were correct as of 1st February 2026.

ii changed its fee structure on the week of index launched, which is not reflected in the numbers - they would move from 7th to 10th most expensive provider. 

How market share is evidenced

Because provider-level Stocks & Shares ISA account counts are not published in the public domain, the methodology uses Censuswide survey responses to indicate market share, ratified against the best available public indicators.

Consumer research

The supplementary research was conducted by Censuswide, among a sample of 1000 UK Investors (who have invested via a platform or app) who invest in a Stocks&Shares ISA. The data was collected in January 2026. Censuswide abides by and employs members of the Market Research Society and follows the MRS code of conduct and ESOMAR principles. Censuswide is also a member of the British Polling Council.

Investor type scenarios

For the press release, the passive / medium / active scenarios are designed to show how platform costs scale with trading frequency. The “active investor” assumptions (6 trades/month and 40% international allocation) are anchored to average UK IG investor behaviour (December 2025) and used as a consistent reference point across providers. Passive (1 trade/month) and medium (3 trades/month) are therefore illustrative comparators, included to provide balance and to demonstrate that the overpayment finding holds under different activity levels. Any monthly subscriber would make at least one transaction per month, making it a realistic ‘most passive’ scenario. 

Provider costs are modelled under different activity scenarios because dealing/FX costs vary with trading activity; the set of 12 ‘highest-cost’ platforms can change by scenario. Each figure shown relates to the scenario stated.