Commission Impact Calculator
Calculate the impact of trading commissions on net profit from trade size, entry, and exit fees.
Returns commission %, break-even, and annual cost.
Trading commission impact quantifies how much brokerage fees and transaction costs reduce your actual investment returns over time. Most retail investors underestimate it badly.
Core formulas: Net Return % = Gross Return % − Total Commission Cost % Break-Even Price (buy) = Purchase Price + (Commission ÷ Shares) Round-Trip Cost = Buy Commission + Sell Commission Annual Drag = Round-Trip Cost × Trades per Year ÷ Portfolio Value × 100
Worked example: stock trade: Buy 100 shares of a stock at $50/share = $5,000 investment. Commission: $9.99 per trade (buy + sell = $19.98 round trip). Stock rises 10%, so you sell at $55/share = $5,500 gross.
Gross profit = $500 Commissions = $19.98 Net profit = $480.02 | Net return = 9.60% (vs. 10% gross)
Commission drag = $19.98 ÷ $5,000 = 0.40% per round trip
Mutual fund expense ratios: the silent compounding killer:
| Fund Type | Typical Annual Expense Ratio | 30-Year Cost on $100k |
|---|---|---|
| S&P 500 index fund (e.g., FXAIX) | 0.015% | ~$4,500 |
| Average actively managed fund | 0.85% | ~$227,000 |
| High-cost managed fund | 1.5% | ~$370,000 |
The 1% difference: $100,000 invested at 7% return for 30 years:
- No fees: $761,226
- 1% annual fee: $574,349
- Difference: $186,877: lost to fees
Modern commission landscape: Most US equity brokers (Fidelity, Schwab, TD Ameritrade) now offer $0 commission trades, but hidden costs remain: payment for order flow, bid-ask spreads, and fund expense ratios. Always calculate the true all-in cost before trading.
The number that actually decides whether a strategy works
Commission as a share of monthly profit is the headline here, but it is the wrong number to design around, because it flatters anyone having a good month. The durable figure is the drag per round trip: cost divided by position size. That is what the stock has to climb before you have made a penny, and it does not care how the month went.
At $9.99 a side on a $5,000 position it is 0.40%, so a trade has to move nearly half a percent to break even. That is survivable for a swing trader holding a week and fatal for a scalper taking 0.3% moves, which is the whole reason the day-trading crowd migrated to zero-commission brokers rather than getting better at trading. Fill in the optional position size above and this page gives you that figure, along with the break-even price per share.
Why zero commission did not make the problem go away
The spread is a cost with no line item. Buy at the ask and sell at the bid on a stock quoted 20.00 by 20.04 and you have paid 0.2% before the price moves at all, which on a $5,000 position is $10, or roughly what the old commission cost. On a liquid megacap the spread is a penny and genuinely negligible. On a thin small-cap it can be wider than any commission ever was. Put your real spread cost into the commission box on this page and the arithmetic still holds.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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