Flat or percentage platform fees: where they cross.

Facts checked 23 October 2026

A percentage platform fee grows with your portfolio; a flat fee stays the same however much you hold. So below a certain portfolio size the percentage fee costs less, and above it the flat fee does. That point is the flat fee divided by the percentage rate. Dealing charges, caps, tiers and fees charged per account all move it, sometimes a long way. This page works through each with invented, round-number tariffs.

What a platform fee is

A platform, or investment platform, holds your investments and runs your ISA, pension or general account. Many charge a yearly fee for that, on top of any charge for buying and selling; some charge none. The fee comes in one of two shapes:

A percentage of what you hold, such as 0.25% a year. Some platforms lower the rate on larger amounts (tiers) or limit the fee to a maximum (a cap).
A flat fee, such as £10 a month, the same on £5,000 as on £500,000.

Fund managers' own charges, the ongoing charges figure of each fund, are separate from the platform's fee and are left out of everything below.

Where a flat fee and a percentage fee cross

Two made-up platforms. Platform P charges 0.25% a year of the value, with no cap. Platform F charges a flat £10 a month, £120 a year. Neither charges for dealing. A year's fee at each portfolio size:

£20,000: P £50; F £120, which is 0.60% of the portfolio.
£48,000: P £120; F £120. This is the crossing point: £120 ÷ 0.25% = £48,000.
£100,000: P £250; F £120, or 0.12%.
£250,000: P £625; F £120, or 0.048%.
£500,000: P £1,250; F £120, or 0.024%.

Below £48,000 the percentage fee is lower; above it the flat fee is. The gap widens as the portfolio grows: at £500,000 it is £1,130 a year.

The same sum works for any pair of tariffs: divide the flat fee for a year by the percentage rate. A flat £60 a year against 0.30% crosses at £20,000; a flat £240 against 0.15% crosses at £160,000.

How dealing charges move the crossing point

Platforms also differ in what they charge for buying and selling, so the yearly fee alone can mislead. Add each platform's dealing charges for a typical year to its fee, then compare.

Suppose Platform F also charges £5 a trade and Platform P charges nothing to deal. At 12 trades a year, F costs £120 + £60 = £180. The crossing point moves from £48,000 to £180 ÷ 0.25% = £72,000. At 48 trades a year F costs £360, and the crossing point is £144,000.

Currency conversion works the same way for anyone buying overseas shares or funds: it is often a percentage of each trade, so it adds to whichever platform charges more for it, in proportion to how much you trade abroad.

Fees charged per account

A flat fee can be charged once for everything you hold at a platform, or for each account. If Platform F charged its £120 for each account, an ISA and a pension there would cost £240 a year, and the crossing point against 0.25% would double to £96,000. A percentage fee charged on the total is the same whether the money is in one account or two.

Caps and tiers

A cap turns a percentage fee into a flat one above a certain size. If Platform P capped its fee on shares, ETFs and investment trusts at £40 a year per account, someone holding only those, in one account, would never pay P more than £40 a year in platform fees, less than F's £120 at every size. Some caps apply only to some kinds of investment, such as shares and ETFs but not funds, so the mix you hold decides whether a cap applies to you.
Tiers usually work like tax bands: each rate applies only to the slice of the portfolio within its band. (Some platforms instead charge the whole balance at the rate of the band it falls in.) A made-up tariff of 0.35% on the first £250,000 and 0.15% on the next £750,000 charges £875 + £375 = £1,250 on £500,000, an overall 0.25%. Against a tiered fee, work out the cost at your own portfolio size rather than reading the top rate.

How to work out what you pay now

Add up a year of charges from your statements and contract notes: the platform fee, dealing charges and any currency conversion. Divide the total by the portfolio's value to get a percentage you can set against another platform's rate. If you hold accounts at more than one platform, do it for each, because each platform applies its own caps and tiers to what it holds. Platforms change their charges, so take any tariff you compare from the platform's own published charges page on the day.

Moving an ISA or a pension to cut costs has costs of its own: exit fees at some platforms, time out of the market, and for some pensions guarantees that would be lost. Those are covered in moving an ISA or SIPP without losing the tax wrapper.

How Fairworth shows it

Fairworth's Platform costs page works out what you pay now, from the accounts you actually hold, your balances and your last 12 months of trades. It then prices the same portfolio at each platform it compares, applying that platform's rules: percentage fees with their tiers and caps, flat monthly and yearly fees, per-trade dealing charges and currency conversion. Where a platform has more than one plan, it uses the plan that covers most of your account types, and the cheapest of those. Balances and trading are pre-filled from your portfolio and can be changed to try a different size or mix. Fund managers' charges, and switching and transfer fees, are not included.

Without signing up, the platform cost comparison shows a year of platform fees, dealing charges and currency costs at the same UK platforms for set portfolios from £50,000 to £2 million, listed A to Z, from the same calculation as the app.