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Commission of $3.50 a side on 0.01 lots: what the statement shows after rounding

Commission of $3.50 a side per lot sounds clear until you trade 0.01 lots. The exact charge is 0.01 x 3.50 = $0.035 a side. Many statements show two decimals, so something has to round.

Three ways the round turn can come out:
Each side rounded up: $0.04 + $0.04 = $0.08
Each side rounded down: $0.03 + $0.03 = $0.06
Calculated on the round turn: $0.07

On a EURUSD 0.01 lot a pip is $0.10, so these are 0.8, 0.6 and 0.7 pips. The first costs 14% more than the exact figure, the second 14% less.

The error is biggest at the smallest sizes. At 0.03 lots the exact side is $0.105, which rounds to $0.11 and gives $0.22 against an exact $0.21, about 5% more. At 0.10 lots the side is $0.35 and nothing needs to round.

If you trade micro lots and track costs in pips, check one fill. A tenth of a pip is 2% of a 5 pip target.

Rounding at 0.01 lot can be a real cost difference. For micro lot scalpers, that 14% matters. Trading 0.02 or 0.03 lots instead of repeated 0.01s can reduce the rounding effect, depending on how the broker rounds. Checking a few rows on the statement against the exact calculation, as you did, shows which method the broker uses.

The rounding bites hardest when a position is built in pieces. Ten separate 0.01 lot entries, each charged $0.04 a side when rounded up, cost 10 x 0.04 x 2 = $0.80 round turn. One 0.10 lot order costs exactly $0.70. The ladder costs 14% more for the same exposure. If the broker rounds down instead, the ladder costs $0.60 and comes out 14% cheaper. In dollars it is a few cents on a trade, but in pips it is 0.8 or 0.6 against 0.7, and for a scalper chasing 3 or 4 pips that gap does show in the monthly total. It is one more reason to know how your broker rounds before choosing between many small orders and one larger one.

A five minute test gives you the rule. Open and close 0.01, 0.02, 0.03, 0.04 and 0.05 lot positions, and read the Commission column in the account history. The exact amounts per side are $0.035, $0.07, $0.105, $0.14 and $0.175. If your history shows $0.04, $0.07, $0.11, $0.14 and $0.18 then the broker rounds half up each side. If it shows $0.03, $0.07, $0.10, $0.14 and $0.17 it rounds down. Check also whether the commission appears on the entry deal, the exit deal or split across both, because MT5 histories can show it in different places. Once you know the pattern you can adjust your cost model instead of guessing.

Compare against a spread-only account. Suppose that account charges a 1.0 pip spread and no commission. The raw account has a 0.1 pip spread plus $0.07 commission on 0.01 lots, which is 0.7 pips, so 0.8 in total. That is 0.2 pips cheaper. If the commission rounds up to $0.08 it is 0.9, and the gap shrinks to 0.1 pip. Halved without anything else changing. For larger sizes the effect disappears because nothing rounds. So an account that is clearly better at 1 lot can be only slightly better at 0.01 lots, and which one to choose can depend on the size you actually trade, not the size in the brochure.

Add one column to the journal: cost in pips, calculated as the spread in pips plus the commission divided by the pip value. For 0.03 lots on EURUSD, the pip value is $0.30. Commission of $0.22 gives 0.73 pips, against 0.70 pips if it were the exact $0.21. Add the spread paid at fill, say 0.2 pips, and the all in cost is 0.93 against 0.90. Do this for twenty trades and you have your real cost per trade at the sizes you use, not a rate card number. If the pip cost turns out to be 10% above what you assumed in your backtest, that is the first thing to correct before asking whether the strategy still works.

Scaling out feels sophisticated. Take half off at the first target, let the rest run. The logic is that profit is secured and the upside remains.

For a scalper, there's a hidden price. The spread is paid on the whole position at entry, and the commission is charged on each closing ticket. Closing in two pieces doubles the number of exit commissions, and on small targets that matters.

The position-size arithmetic also bites. At 0.02 lots, half is 0.01, the minimum. There's no room to scale further, and rounding can distort the split.

The psychological effect is mixed. Banking half the profit gives comfort, and the remaining half is managed with less stress. But it also tends to shorten the average winner, since the second half gets closed early out of nervousness.

The result of the whole exercise often looks the same as trading half size with a single exit, except for the extra cost.

A test over a few hundred trades, comparing a single exit with a scaled one using real costs, settles the question.

Did scaling out improve the real results once costs were included?