Ask most people what determines how much their investments grow and they'll say "picking the right ones." Fair enough — but there's a second factor that's far more predictable and entirely within your control: what you pay to invest. Fees are the silent passenger on every portfolio, and over an investing lifetime they decide a startling share of where you end up.
The maths nobody shows you
Here's why a number that looks tiny isn't. Imagine two investors who both put money in and earn the same 7% a year before costs over 30 years. One pays total fees of 0.2% a year; the other pays 1.2% — a single percentage point apart, the kind of gap that sounds trivial in a sales brochure.
That one point, compounded over three decades, can quietly swallow somewhere around a quarter to a third of the final pot. Not a third of the fees — a third of the money. The reason is compounding working in reverse: every pound paid in charges is a pound that never gets to grow, and then never gets to grow on its growth. The fee feels small each year. The cumulative cost is enormous.
The fees you're actually paying
UK investors usually face two separate layers, and it pays to know both.
- The platform (or account) fee. What your investment platform charges to hold your ISA or pension. Some charge a percentage of your holdings; others charge a flat annual or monthly fee. Which is cheaper depends entirely on your pot size — more on that below.
- The fund charge (the OCF). The Ongoing Charges Figure is what the fund itself takes each year, baked into the price so you never see it leave your account. A global tracker fund might have an OCF around 0.1–0.2%. An actively managed fund is commonly 0.6–1% or more.
There can be more buried underneath — trading costs inside the fund, exit or transfer fees, charges for buying individual shares. But the platform fee and the OCF are where the big, ongoing money sits.
The percentage-versus-flat trap
This is the decision that catches people out as their pot grows. A platform charging 0.45% of your holdings costs £45 a year on £10,000 — perfectly reasonable. On £200,000, that same 0.45% is £900 a year for essentially the same service. Meanwhile a flat-fee platform might charge a fixed sum regardless of size.
So the rule of thumb: when your portfolio is small, percentage-fee platforms are often cheapest. As it grows into six figures, a flat-fee platform frequently wins, sometimes by hundreds of pounds a year. Reviewing this as your balance climbs is one of the highest-value hours you'll ever spend on your finances.
How to cut what you pay
None of this requires being clever about markets. It just requires paying attention.
Favour low-cost index funds for the core. Decades of evidence show that most actively managed funds fail to beat a simple low-cost tracker after fees, especially over the long run. You don't have to go all-in on trackers, but using them for the bulk of your portfolio keeps the OCF down where it belongs.
Match your platform to your pot. Check whether percentage or flat fees suit your balance now, and re-check whenever it changes meaningfully. Transferring an ISA or pension between platforms is more straightforward than it used to be, though check for exit fees before you move.
Use your ISA and pension allowances. Cutting fees and cutting tax are the two reliable wins in investing. A stocks-and-shares ISA shelters up to £20,000 a year from tax on growth and income; pension contributions get tax relief on the way in. Both stretch your real return further with no extra risk.
Read the OCF before you buy, every time. It's published for every fund. Two funds tracking the same global index can charge wildly different amounts for an almost identical product. There is rarely a good reason to pay the higher one.
The honest takeaway
You can't control whether markets rise or fall next year. You can control, precisely and permanently, how much you hand over in fees — and over a 30-year horizon that control is worth more than most stock-picking ever will. Spend an afternoon finding out exactly what you pay across both layers. For a lot of investors, it's the most profitable afternoon of their year.