Position Sizing on a Small Account
The constraint is the step, not the percentage
New traders are told to risk 1% per trade, and on a small account that advice quietly stops working. Take a 100 USD account. One percent is 1.00 USD. Put the stop 20 pips away on EUR/USD and the formula asks for:
Five hundred units is half a micro lot. Most brokers deal in steps of 0.01 lots — one thousand units — and the rule is that you round down. Half of 0.01 rounds down to zero. The correct size for that trade, at that risk, on that account, is no trade at all.
This is not a rounding nuisance. It is the reason small accounts drift into over-risking: the size the formula produces is untradeable, so the trader raises the percentage until the number clears the minimum, and in doing so takes three or four times the risk the plan called for.
What is actually tradeable at 1% risk
The table below applies the formula to four account sizes at 1% risk, on EUR/USD with a USD account, before spread and commission, with a 0.01-lot minimum step. Each cell gives the rounded-down size and the loss it produces if the stop is hit.
| Account | 1% risk | 10-pip stop | 20-pip stop | 50-pip stop |
|---|---|---|---|---|
| 100 USD | 1.00 | 0.01 lot — 1.00 USD | not tradeable | not tradeable |
| 250 USD | 2.50 | 0.02 lot — 2.00 USD | 0.01 lot — 2.00 USD | not tradeable |
| 500 USD | 5.00 | 0.05 lot — 5.00 USD | 0.02 lot — 4.00 USD | 0.01 lot — 5.00 USD |
| 1,000 USD | 10.00 | 0.10 lot — 10.00 USD | 0.05 lot — 10.00 USD | 0.02 lot — 10.00 USD |
Read the 250 USD row across: a 10-pip stop and a 20-pip stop both land on 2.00 USD of actual risk, because the step is too coarse to express the difference. The plan said 2.50 and the broker can only give you 2.00. Rounding down costs you a quarter of your intended risk, which is annoying but harmless. Rounding up to 0.03 lots would cost you 3.00 — half again over budget — and that is the habit that compounds.
Costs eat a small budget faster
Commission is charged per volume, not per account size. At 7 USD per standard lot round turn, one micro lot costs 0.07 USD. Against a 1.00 USD risk budget that is 7% of the trade gone before the market moves. Against a 100.00 USD budget on a 10,000 USD account it is 0.07%.
The same applies to the spread. One pip of spread on a 0.01-lot position is 0.10 USD — a tenth of a 1.00 USD budget. Add both to a 20-pip stop and the effective stop distance grows by five percent, which shrinks the size you can afford by five percent, which makes the step problem worse rather than better.
The lot size walkthrough shows the same effect on a 5,000 USD account, where the shortcut answer overshoots the budget by nearly 7% purely by ignoring these two costs.
What actually helps
- A broker with a smaller step. A 0.001-lot step — one hundred units, sometimes called a nano lot — makes 500 units tradeable, and the 100 USD / 20-pip trade at the top of this page becomes possible at 1% risk. This is the single change that removes most of the problem.
- Instruments with finer granularity. Crypto futures in this reference data step in 0.001 contracts, and stocks trade in whole or fractional shares. The step is the constraint, so choose where the step is small. The share sizing guide covers the fractional-share case.
- Fewer, better-defined trades. If a 50-pip stop is untradeable at your size, the honest answer is that this particular setup is not available to you, not that the risk percentage should double.
- Accept under-risking while the account is small. Rounding down to 2.00 when the plan said 2.50 costs nothing but opportunity. Rounding up costs the account.
What does not help
- Raising the percentage to clear the step. Going from 1% to 3% on a 100 USD account makes the 20-pip trade possible — 3.00 / 0.0020 = 1,500 units, which rounds down to 0.01 lots. It also triples your risk per trade, and the losing streak tables show what that does to a small balance over twenty losses.
- Tightening the stop until the size fits. It works arithmetically — a 5-pip stop on a 100 USD account at 1% gives 2,000 units — but the stop is now inside normal noise, so the trade loses far more often than the plan assumed. The size fits; the strategy does not.
- Ignoring the step because the platform accepts the order. Some platforms accept a size and silently round it. Check the filled volume, not the requested volume.
The one number to check before every trade
Before you place an order on a small account, divide your risk budget by the stop distance and compare the answer to your broker's minimum step. If the answer is smaller than the step, the trade is not available at that risk — and the fix is a different broker, a different instrument or a different trade, never a bigger percentage.
Related guides
- Lot sizes explained — standard, mini, micro and nano lots, and what one pip is worth in each.
- How much should you risk per trade? — the arithmetic behind choosing the percentage in the first place.
- Position sizing for gold — an instrument where the step is one whole ounce.
- How to calculate position size in forex — the full formula and the four inputs.