What this calculator does
Takes portfolio value, annual contributions, gross return, and fee structures for up to three platforms (flat fee or percentage-based). Shows the projected portfolio value and total fees paid over the selected time horizon for each platform, so you can see the long-term cost of fees on compounding growth.
The formula
For a percentage-based fee structure: Net return = gross return − total annual fee % Where total annual fee = platform fee % + fund OCF % FV (net) = P × (1 + r_net)^t + C × [(1 + r_net)^t − 1] / r_net For a flat annual fee structure: Each year: V(t+1) = (V(t) + C) × (1 + r_gross) − flat_fee Total fees paid = gross FV − net FV (cumulative opportunity cost of the fee, including lost compounding)
Assumptions
- Annual contributions are made at the start of each year.
- Fees are deducted at the end of each year.
- Gross return is constant throughout the projection.
- Flat fees are fixed in nominal terms — they are not adjusted for inflation.
Data sources
No regulatory data is used. The calculator applies standard compound growth formulae. Fee structures are user-entered; the calculator does not pull live platform pricing. Always verify current fee schedules directly on the provider's website before making investment decisions.
Limitations
- Does not include dealing charges, trading commissions, or foreign exchange costs.
- Flat fees are modelled in nominal terms and do not increase with inflation.
- Does not account for ISA allowance limits on annual contributions.
- Actual platform fee structures vary (for example, tiered percentage fees, fee caps) and may change over time — always verify current pricing on the provider's website.
- Does not model fund switching costs or exit fees.
Worked example
Inputs: £50,000 portfolio, no additional contributions, 8% gross return, 20 years.
Platform A: 0.25% annual fee (net return 7.75%) FV = £50,000 × (1.0775)^20 = £50,000 × 4.392 = £219,600 Total fees paid: approx £25,300 Platform B: 0.65% annual fee (net return 7.35%) FV = £50,000 × (1.0735)^20 = £50,000 × 4.122 = £206,100 Total fees paid: approx £38,800 Cost of choosing Platform B over A: £13,500 over 20 years
Changelog
| Date | Change |
|---|---|
| May 2026 | Initial publication |