Investment Return Calculator: See the Fee Drag
This free calculator projects how your investments could grow from a lump sum and regular monthly contributions — and, crucially, how much an annual platform fee quietly takes along the way. Enter your numbers to see your projected pot with and without fees, the total fees paid, and the difference. A fee that looks tiny each year compounds into a surprisingly large sum over decades. Projections are illustrative only, not advice.
Reviewed by Yaniv Barshaf · Fees verified June 2026 · Our methodology
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Investment return & fee drag calculator
See how your investments could grow — and how much a platform fee quietly eats along the way. A fee that looks tiny each year compounds into a real sum over decades.
Projected value (after fees)
£139,458
If fees were 0%
£144,573
Total you paid in
£58,000
Lost to platform fees over 20 years
£5,115
A 0.25% annual fee costs you £5,115 of final value — £3,046 paid in fees, plus the growth those fees would have earned.
Illustrative projection only — not financial advice. Returns are assumed to be constant and are not guaranteed; real markets rise and fall, and you may get back less than you invest. Figures assume monthly compounding and that the platform fee is charged on your balance each month. It does not model inflation, tax, fund charges or dealing costs. Capital at risk. This is not financial advice. Investing involves risk of loss.
How the return calculation works
Enter your starting lump sum, your monthly contribution, an expected annual return, the number of years, and your platform's annual fee percentage. The calculator compounds your balance monthly: it applies one twelfth of your expected return, adds your contribution, then deducts one twelfth of the annual fee from the resulting balance — repeating for every month of the period. It runs the same projection twice, once with your fee and once at 0%, so you can see the fee drag in cash: the difference in final value, plus the total fees actually deducted along the way. Returns are assumed constant for illustration; real markets are volatile and never move in a straight line. The tool does not model inflation, tax, fund charges (the ongoing cost of the ETFs or funds themselves) or dealing commissions — it isolates the platform-fee effect so you can see it clearly.
Why a 0.25% fee is not small
Platform fees are charged on your whole balance, every year, which is why a number that reads as a rounding error compounds into real money. On a portfolio built from £10,000 plus £200 a month over 20 years at 7%, a 0.25% annual fee costs noticeably more than the fees themselves — because every pound taken in fees is also a pound that stops compounding. Raise the fee to 1% and the drag can run into five figures over a working lifetime of investing. This is the single strongest argument for low-cost platforms: the return you assume is a guess, but the fee is a certainty you control. Once you have your target platform, run its real fee through this tool, then use the FX fee calculator and trading cost calculator to check the per-trade costs it does not capture.
Frequently Asked Questions
What return should I assume?
There is no correct figure — it is your assumption, not a forecast. A globally diversified equity portfolio has historically returned roughly 5-8% a year on average over long periods, but with large ups and downs, and the past does not predict the future. Try a range of values to see how sensitive your projection is. This is illustrative, not advice.
How is the platform fee applied?
The calculator deducts one twelfth of your annual fee percentage from your balance each month, mirroring how most platforms charge. Because the fee is taken from your whole pot every month, it compounds against you — which is why the final fee drag is larger than the simple sum of fees paid.
Does this include fund charges or trading costs?
No. It isolates the platform (account) fee so you can see its effect clearly. Your funds or ETFs have their own ongoing charges, and buying and selling can incur commission and FX fees — use the FX fee calculator and trading cost calculator on this site to estimate those separately.
Is the projected value guaranteed?
No. It is an illustration based on the constant return you enter, which real markets will not deliver in a straight line — some years are negative. You could get back less than you invest. Treat the output as a way to understand compounding and fee drag, not as a promise of what your investments will be worth.
Does the calculator account for inflation or tax?
No. Figures are in nominal pounds before inflation, and before any tax. Inflation reduces the real spending power of your final pot, while a Stocks and Shares ISA can shelter gains from tax. Both matter for real-world planning but sit outside this tool's scope. Not financial advice.