The most common mistake UK investors make is assuming one platform is “cheapest.” In reality, the cheapest platform depends almost entirely on the size of your portfolio.
Two fee models
Most UK investment platforms use one of two approaches:
Percentage fee: You pay a percentage of your portfolio annually. If you have £10,000 invested and pay 0.45%, that’s £45/year. If your portfolio grows to £100,000, you pay £450/year — ten times more for roughly the same service.
Flat fee: You pay a fixed monthly or annual subscription. Interactive Investor charges £11.99/month (£143.88/year) regardless of whether you have £20,000 or £2,000,000 invested.
The crossover
These two models intersect at a “crossover point.”
For HL vs ii (the most common comparison), the crossover for a funds ISA is around £50,000:
- Below £50,000: HL’s percentage fee is lower than ii’s flat fee
- Above £50,000: ii’s flat fee is lower than HL’s percentage fee
At £100,000 with HL, you’re paying approximately £450/year. With ii, it’s still £143.88/year — a saving of over £300/year.
It gets more complex
The crossover isn’t a single number. It shifts based on:
- What you’re investing in: Shares and ETFs on HL are capped at £45/year, which changes the calculation significantly
- How often you trade: Flat-fee platforms often include free trades, but charge per trade beyond that
- Account type: SIPP fees are often different from ISA fees
Use our fee calculator to find the exact crossover for your specific situation.
Key crossover points (funds ISA, monthly trading)
| Comparison | Crossover |
|---|---|
| HL vs Interactive Investor | ~£50,000 |
| HL vs Vanguard | ~£83,000 |
| AJ Bell vs Interactive Investor | ~£58,000 |
These are approximate and assume monthly trading. Use the calculator for exact figures.
Fee estimates based on published rates as of April 2026. Always verify current fees directly with your provider.