Decision Lab
Three practice cases on the arithmetic of a trade plan: what leverage changes, what commission does to a fixed risk budget, and how a late fill or a currency conversion can push a loss past the plan. Each case asks for a prediction and how sure you are, shows the answer worked out by the calculators' own code, explains it, then sets a fresh variation with new numbers.
The cases test how a plan's numbers are read. They do not measure trading skill or readiness to trade, and nothing is stored: answers stay on this page and clear when it reloads. Every case uses a USD account, the calculators' fixed reference prices and a 0.01-lot minimum and step, measures the stop from the entry fill price and leaves out swap.
1. The same position at different leverage
Leverage decides how much margin a position holds. The question is what else it changes.
1.00 lots of GBP/USD at 1.3335 on a USD account. The account's leverage goes from 1:100 to 1:300; the position stays the same size.
2. Commission against a fixed risk budget
A size worked out from the stop alone has room for a per-lot commission only when rounding down happens to leave enough.
A $2,000 USD account risks 1% ($20.00) on EUR/USD at 1.1253 with a 20-pip stop, where a pip on 1 lot is worth $10.00. The plan divides the budget by the loss per lot at the stop (20 pips × $10.00) and rounds down: 0.10 lots. The broker charges $7.00 per lot, round trip.
3. When the loss passes the plan
With a standard stop, the loss at the stop is a plan, not a cap: a late fill or the currency conversion can move it.
A short position of 2.00 lots of USD/JPY at 158.02 on a USD account has a 50-pip stop at 158.52. The loss is in yen and converts into dollars at the USD/JPY price.
The same arithmetic runs in the Margin Calculator and the Position Size Calculator, and the position sizing article works through it step by step.