A stock’s price return does not tell you what your actual holding earned after fees and sales. To compare that holding with an ETF, give the alternative the same purchase budget, state the sale rule, and keep the sold shares separate from the shares you still own.
This guide is for IBKR investors who hold individual stocks, whether or not they also own ETFs. You do not need a long account history, an account with PerfectPerf, or an email address to use it.
Download the published example inputs (CSV) to use the same numbers in a spreadsheet. These are fictional teaching inputs, not IBKR data or an import template. The file contains the guide’s fixed example. It does not export changes made in the separate comparator.
01 / Start with the actual cost
A $1,000 purchase costs $1,010.
Buy 100 shares at $10 each, then add the $10 purchase fee. You spend $1,010 on shares initially worth $1,000. The fee is part of the starting cost, so the return begins slightly below zero.
Where the purchase budget goes
The ETF receives the same total budget and pays the same dollar fee. At the same $10 starting price, it also buys 100 units.
02 / Separate what you sold
One purchase branches into two parts.
On 2 February, sell 40 of the 100 shares at $12. The sold shares take 40% of the original acquisition cost with them. The other 60% stays with the shares you still own.
A closed part means some shares were sold, even while the position remains open. This proportional allocation is a performance convention, not a tax-lot calculation. With several purchases, the underlying position method uses average acquisition cost.
03 / Compare like with like
Two parts. Two finish lines.
By 2 March, the remaining 60 shares are worth $780 at $13 each. Their $174 gain on $606 of cost gives a cumulative 28.71% return. The shares sold in February keep their earlier result.
Focus on a finish line
Same prices, same fees, same sale fraction.
2 Jan → 2 Feb 2026
Closed part
40 shares sold
Stock − ETF0.00 pp
- Allocated cost
- $404.00
- Net sale proceeds
- $478.00
- Gain on each side
- $74.00
2 Jan → 2 Mar 2026
Open part
60 shares still held
Stock − ETF0.00 pp
- Allocated cost
- $606.00
- Remaining value
- $780.00
- Gain on each side
- $174.00
The identical prices make the stock and synthetic ETF equal here: 0.00 percentage points apart on both parts. The later price changes only the shares still held, never the return already realized on sold shares.
04 / Know what this comparison answers
Equal inputs are a useful check, not a claim of outperformance.
In the published example, identical stock and ETF prices, the same fees and the same sale fraction produce a 0.00 percentage-point difference for both parts. That is a consistency check. It does not show that stock-picking, an ETF, or PerfectPerf will outperform.
- Purchase budget
- The ETF gets the stock’s total acquisition cost. The same dollar purchase fee is deducted before buying ETF units at the synthetic ETF price. Fractional ETF units are allowed. At baseline, ($1,010 − $10) ÷ $10 = 100 units.
- Partial-sale rule
- Both sides sell the same proportion on 2 February and incur the same dollar sale fee. This is a matched-fraction comparison; it does not promise identical sale proceeds or identical total cash flows when the prices differ.
- Return and difference
- For each part, return = (value or net proceeds − allocated cost) ÷ allocated cost. The open value is a valuation, without an assumed final sale fee. Difference = stock return minus ETF return, expressed in percentage points. Calculations retain precision; displayed amounts and percentages are rounded.
- Period and limits
- The closed part runs from 2 January to 2 February; the open part runs from 2 January to 2 March 2026. Returns are cumulative, not annualized. This is one position, not a whole-portfolio TWR or MWR. Adding or averaging position returns does not reconstruct a portfolio return.
Whole-portfolio analysis also needs external deposits, withdrawals, cash and the timing of valuations. It is a separate question from whether one position beat a passive alternative. Broader portfolio analysis in PerfectPerf is planned; this guide does not imply it is available today.
The example also differs from “what if I had kept every share?” Here, the sale happens on both sides. A purchase-conservation simulation would retain the original purchase independently of later real sales and answer a different question.
Sources and further context
The arithmetic above is PerfectPerf’s stated illustration, rather than a claim that a broker or regulator prescribes this exact benchmark convention.
- SEC Investor.gov: How fees and expenses affect your investment portfolio. Transaction fees and ongoing expenses are different costs; both matter when interpreting real returns.
- SEC Investor.gov: Mutual fund and ETF fees and expenses. Our synthetic ETF omits ongoing fund expenses; a real ETF comparison must account for its actual price and distribution conventions.
- Interactive Brokers: PortfolioAnalyst features. IBKR already offers portfolio analysis and benchmark comparisons. This guide focuses on the separate, inspectable position-level example above.
Sources checked 17 October 2026. Educational illustration; no security, fund or investment strategy is recommended.