The most common mistake UK investors make is assuming one platform is the cheapest. In reality, which platform costs least depends almost entirely on the size of your portfolio — and the exact point where this flips is the crossover.
Two fee models
Most UK investment platforms use one of two approaches:
Percentage fee: You pay a fraction of your portfolio each year. If you have £10,000 and pay 0.35%, that’s £35/year. If your portfolio grows to £100,000, you pay £350 — ten times more for broadly the same service.
Flat fee: You pay a fixed subscription. Interactive Investor’s Core plan charges £5.99/month (£71.88/year) whether you have £20,000 or £100,000 invested.
Zero fee: Barclays, InvestEngine, Trading 212, and Freetrade charge no platform fee at all.
How the crossover works
Because percentage fees rise with your portfolio while flat fees stay fixed, there’s always a point at which the flat fee becomes cheaper. That’s the crossover.
The formula:
Crossover portfolio size = (Flat total annual cost − Percentage platform’s dealing costs) ÷ Percentage rate
For HL funds vs Interactive Investor Core (both with monthly trading):
- ii Core total: £71.88 + (12 × £3.99) = £119.76/year
- HL dealing cost: 12 × £1.95 = £23.40/year
- Crossover: (£119.76 − £23.40) ÷ 0.0035 = ~£27,500
At £27,500, both platforms cost roughly the same. Below that, HL’s percentage is lower. Above it, ii’s flat fee wins.
Key crossover points (ISA funds, monthly trading, June 2026)
| Comparison | Crossover |
|---|---|
| HL (0.35% + £1.95/trade) vs ii Core (£71.88 + £3.99/trade) | ~£27,500 |
| Fidelity (0.35%, no dealing) vs ii Core | ~£34,000 |
| AJ Bell (0.25% + £1.50/trade) vs ii Core | ~£41,000 |
| Vanguard (0.15%, min £48/yr) vs ii Core | ~£80,000 |
| HL vs ii Plus (£179.88 + £1.49/trade) | ~£55,000 |
ii Core is limited to portfolios up to £100,000. For larger portfolios, compare against ii Plus.
Note: these crossovers shifted significantly in 2026. HL’s fee cut (0.45%→0.35%) and ii’s restructure (£143.88→£71.88 Core) both moved the HL vs ii crossover from approximately £32,000 down to approximately £27,500.
For an up-to-date calculation at your exact portfolio size, use our fee calculator.
Dealing fees shift the crossover
The crossover isn’t just about platform fees. Dealing charges matter too.
- HL now charges £1.95 per fund trade — 12 monthly trades cost £23.40/year, narrowing the gap with flat-fee platforms
- Fidelity still charges £0 per fund trade, so its crossover with ii Core is purely the platform fee ratio
- ii Core charges £3.99 per trade with no free trades — 12 monthly trades add £47.88/year
- Barclays charges £0 for fund dealing — no crossover needed, it’s free at any portfolio size
The Barclays effect
Since June 2026, Barclays removed its platform fee and charges nothing for fund dealing. For fund investors, Barclays is free at any size and there’s no crossover to calculate — it’s simply the cheapest.
The crossover concept still matters for ETF and share investors (where Barclays charges £6/trade) and for anyone comparing platforms that still charge platform fees.
The ETF exception
Crossovers work differently for ETF investors because some platforms cap their charges:
- AJ Bell caps ISA ETF fees at £42/year
- HL caps ISA ETF fees at £150/year (raised from £45 in March 2026)
- Freetrade, InvestEngine, Trading 212 charge £0
For ETF investors, Freetrade/InvestEngine/Trading 212 are always cheaper than any capped platform. The crossover concept doesn’t really apply when free options exist.
As your portfolio grows
The crossover isn’t a one-time calculation. As your portfolio grows through contributions and returns, you may cross the threshold without noticing.
At £30,000 in funds, HL (0.35%) costs roughly £105 + £23 = £128/year and ii Core costs £120/year — they’re nearly level. At £50,000, HL is £198 vs ii’s £120 — a £78/year gap. At £100,000, HL is £373 vs ii’s £120 — a £253/year gap.
On a £100,000 portfolio, the gap between HL (£373/year) and ii Core (£120/year) is £253/year. Invested and compounding at 7% for 20 years, that saving is worth approximately £11,000 in additional wealth.
Fee estimates based on published rates as of June 2026. Always verify current fees directly with your provider.