The seat belt comes first
Imagine planning a journey before checking the brakes. Choosing trade size before defining the loss budget creates a similar problem. Today we will not place a live order. A hypothetical example takes us from a cash loss budget to an allowable position. We will also see when the smallest permitted position is still too large. The photographs provide context; our inputs are not taken from a live account. The deliverable is a reviewable calculation, not a trading recommendation.
Loss budget → stop distance → size
Risk budget is not margin
In an imaginary two-thousand-dollar account, half a percent equals ten dollars. That is an arithmetic example, not a suitable percentage for everyone. Margin supports a position; the risk budget concerns an adverse price move and costs. More leverage can reduce required margin without reducing the loss from the same movement on the same position. Available margin therefore does not establish acceptable risk. Calculate the exposure separately rather than using the largest size the platform permits.
2000 × 0.005 = $10 Margin ≠ maximum loss
Use the actual contract
Check the actual symbol specification: contract size, minimum volume, volume step, tick size and tick value. One memorized formula is not reliable across every instrument. The loss estimate must respect the contract and account currency. MetaTrader provides a profit-estimation function, but commission and execution assumptions need separate attention. Specify the entry and exit quotes used so an included spread is not counted twice. Invalid inputs must stop the calculation rather than produce an apparently precise size.
Minimum • step • tick • account currency Do not double-count costs
Example one: round down
The hypothetical budget is twenty-five dollars. Estimated stop loss is two hundred fifty dollars per lot and additional round-trip costs are ten dollars per lot. Divide twenty-five by two hundred sixty to obtain about zero point zero nine six lots. With a zero point zero one step, round down to zero point zero nine. Estimated risk is twenty-three dollars and forty cents. Rounding up to zero point one creates twenty-six dollars of estimated risk and violates the budget.
25 / 260 ≈ 0.09615 0.09 → $23.40; not 0.10
Wider stops and minimum size
If one-lot stop loss rises to five hundred dollars and costs remain ten, the same budget allows less size. Divide by five hundred ten and round down to zero point zero four lots: estimated risk twenty dollars and forty cents. If the minimum is zero point zero five, skip the trade instead of arbitrarily moving the stop. Both volume step and minimum must be respected. This example assumes costs scale with volume; minimum or nonlinear fees require a different calculation.
25 / 510 → 0.04 lots Minimum 0.05? Skip
R multiples and combined exposure
Define one R before entry, for example the planned loss after size rounding and stated costs. With R equal to ten dollars, a twenty-dollar gain is two R and a fifteen-dollar loss is minus one point five R. Several trades may share the same market driver. Adding planned loss budgets does not guarantee the actual worst-case loss. Gaps and slippage can exceed the plan. Combined exposure and the decision to stop new entries require separate rules.
+20 / 10 = +2R -15 / 10 = -1.5R
Exercise and answer
Pause and calculate using an eighteen-dollar budget, one-lot stop loss of three hundred and costs of twenty per lot. The step is zero point zero one. Raw size is zero point zero five six two five, and rounding down gives zero point zero five lots with estimated risk sixteen dollars. Change minimum volume to zero point one and the answer becomes no trade. Record inputs, raw size, permitted size and rejection reason in the worksheet.
18 / 320 = 0.05625 Size 0.05; risk $16
