I passed my first challenge feeling like a genius, then spent two months on the funded account slowly bleeding. Same strategy, same risk — but the balance sagged a little every day, like a tyre with a slow puncture. When I finally added up a month of spreads, commissions and swaps, I had been paying for a second losing strategy I never chose to trade. My edge was real. My costs were eating it.
In this article
That is why I built the Trading Cost and Drawdown Calculator at the top of this page. You give it your spread, pip value, lots per day, commission and swap, and it shows what your trading really costs: per day, per month, per trade — and, the number that matters on a prop account, what share of your daily loss limit those costs consume. Let me explain the maths, then show you the month that taught me the lesson.
Costs are a position you hold every day
Every trade you open starts underwater. The spread takes its cut the moment you enter, the commission takes its cut on the way in and out, and swaps take a little more for every night you hold. None of it feels dramatic. That is the danger — it is a drip, not a flood, and drips add up.
On a prop account there is a second problem: costs come out of the same equity your daily limit measures. A $5,000 daily limit with $66 of daily costs is really a $4,934 limit for your strategy. The firm does not carve costs out for you. So I measure costs as a share of the daily limit, and I get nervous when that share climbs past 20% — the calculator warns you at that line.
The maths behind your real daily cost
| Variable | What it is | Typical value |
|---|---|---|
| Spread (pips) | Your average spread on the symbols you trade | 0.5 – 3.0 pips |
| Commission | Round-turn commission per lot | $0 – $7 |
| Lots per day | Total volume you trade on a normal day | 1 – 10 lots |
| Cost in R | What one trade’s cost is worth in risk units | Keep under 0.1 R |
Cost in R is the figure that connects to your edge. If your plan earns 0.25R per trade on average and each trade costs 0.1R, costs are taking 40% of your expectancy. Expressing the cost in the same units as your edge is what finally made the leak visible to me.
The $1,320 month that taught me the lesson
Here is the default example the calculator ships with — close to my own numbers from that bleeding summer. $100,000 account, 5% daily limit, 1.5 pip spread, $10 pip value, 3 lots a day, $7 round-turn commission, no swaps, 20 trading days, 0.5% risk per trade.
| Step | Calculation | Result |
|---|---|---|
| Spread cost per day | 1.5 × $10 × 3 lots | $45.00 |
| Commission per day | $7 × 3 lots | $21.00 |
| Daily trading cost | $45 + $21 + $0 | $66.00 |
| Share of daily limit | $66 ÷ $5,000 | 1.3% |
| Monthly cost | $66 × 20 days | $1,320.00 |
| Cost per trade | $66 ÷ 3 lots | $22.00 |
| Cost per trade in R | $22 ÷ $500 risk | 0.044 R |
At 1.3% of the daily limit, this is a healthy setup — well under my 20% warning line. My real problem back then was different: I was scalping gold with wide spreads and taking six trades a day. Run the same maths at 3 pip spreads, 6 trades and $7 commission and the daily cost jumps past $400 — over 8% of the limit every single day, before a single trade has won or lost. Over a month that was a five-figure leak I had mistaken for bad luck.
Using the cost calculator step by step
Fill the fields at the top of this page, then press Calculate.
| Input field | What to enter | Sample figure |
|---|---|---|
| Account size ($) | Your starting balance | 100000 |
| Daily loss limit (%) | Your firm’s per-day ceiling | 5 |
| Spread (pips) | Your average spread, not the best-case one | 1.5 |
| Pip value per lot ($) | Per-lot value on your main symbol | 10 |
| Lots traded per day | Total volume on a normal day | 3 |
| Commission per lot, round-turn ($) | Both sides included | 7 |
| Swap per night ($) | What you pay to hold overnight | 0 |
| Trading days per month | How often you trade | 20 |
| Risk per trade (%) | Your fixed plan percentage | 0.5 |
Everything is calculated in your browser, and nothing is stored.
Keeping costs inside the 20% line
The 20% warning is my own rule, not a firm rule: if my daily costs exceed a fifth of my daily limit, the plan is too expensive for the account and something has to change. Usually the fix is not heroic — it is boring. Fewer trades, wider targets, cheaper symbols, or a broker with tighter pricing on what I actually trade.
Three habits keep me under the line. First, I enter my average spread, not the advertised minimum — spreads widen around news, as news trading and daily drawdown explains. Second, I count commission round-turn and never forget the swap on swing trades. Third, I re-run this calculator whenever I change symbols, and pair it with the Floating Loss Drawdown Calculator to see costs and open risk together.
And the mindset part: I set my personal daily stop below the firm limit by at least my daily cost, because the firm’s limit assumes a frictionless world and I trade in this one. For a neutral reference on what trading costs include, the Investopedia guide to transaction costs covers the components well.
Questions traders ask about trading costs and drawdown
How much of my daily limit should costs use?
I aim for under 10% and treat 20% as the hard warning line. Above 20%, costs are no longer a rounding error — they are a second strategy working against you every day, and the plan needs cheaper execution or fewer trades.
Why express the cost in R?
Because your edge is measured in R too. A $22 cost means nothing on its own, but 0.044R against a 0.25R expectancy means costs take nearly a fifth of your edge. Same units, honest comparison.
Do swaps really matter on a prop account?
On day trades, no. On swing trades held for weeks, absolutely — a few dollars a night times twenty nights is real money, and it counts against the same daily equity the firm watches. Enter your real swap instead of zero if you hold overnight.
Should I use the minimum spread or the average?
The average, always. The minimum is marketing. Watch your platform for a week, note the spread at the times you actually trade, and use that number. Around news, assume worse.
Can high costs alone breach a daily limit?
Rarely alone, but they shrink the margin for everything else. A $400 daily cost on a $5,000 limit means one normal losing day plus costs can finish you. Costs do not cause the breach — they make the breach cheaper to reach.
