Lesson 7 Position Sizing and Exposure

Convert a demo loss budget into units, include costs, round sizes appropriately, and recognise shared currency exposure.

Start with the invalidation point

A stop location should express where the idea is considered invalid under the test rules. After choosing that location, adjust the position size to the loss budget. Moving a stop closer simply to permit a larger position changes the trade hypothesis and may make it inconsistent with the plan. For the course, use these illustrative demo limits: planned loss no more than 0.5% of current equity per trade, total planned loss across open positions no more than 1%, a 1% session loss threshold, and a 3% weekly loss threshold. These are teaching constraints, not proven optimal or universally suitable levels. Real losses can exceed planned figures. Measure the session or weekly threshold from the relevant starting equity, including realised and floating loss and charges, with deposits and withdrawals excluded. At a threshold, close practice exposure and cancel pending entries under the demo plan, stop for the period, and review. Gaps and slippage can carry a loss beyond the threshold; the threshold is an action rule, not a guarantee.

A basic calculation

Loss budget = current equity × chosen fraction. With 2,000 USD equity and 0.5%, the budget is 10 USD. If EUR/USD has a 25 pip distance from the expected executable entry to the stop’s executable price, and a standard lot is 10 USD per pip, the price loss per standard lot is 250 USD. Ignoring all additional costs gives 10 ÷ 250 = 0.04 lots, or 4,000 EUR. This is only the starting estimate.

Include separate costs and an execution allowance

Assume a 7 USD round trip commission per standard lot and a 2 pip adverse slippage allowance. The estimated loss per lot becomes: 25 × 10 + 7 + 2 × 10 = 277 USD. The size ceiling is 10 ÷ 277 ≈ 0.0361 lots. If the platform’s size increment is 0.01 lots, round down to 0.03 lots, or 3,000 EUR. Estimated loss is 0.03 × 277 = 8.31 USD. Rounding up to 0.04 produces an estimate of 11.08 USD and exceeds the budget. Here the stop distance already runs from an expected entry fill to an expected exit price, so the spread is embedded in that distance. Do not add it again. A calculation based on chart midpoints must first be adjusted for the relevant executable prices. The 2 pip allowance is a modelling assumption; adverse slippage can be larger. When fees have fixed minimums or nonlinear tiers, solve using the actual fee schedule. For other quote or account currencies, first convert pip value to account currency. Check the provider’s sizing preview independently.

When the minimum is too large

Suppose a budget is 1 USD, a 30 pip stop is required, and the smallest position is 1,000 EUR in EUR/USD. The price loss alone is 3 USD. The correct course decision is skip the trade or use paper practice. Do not increase risk or distort the stop to force an order.

Account for related positions

Buying EUR/USD and GBP/USD both creates short USD exposure. They are separate trades with a shared risk factor. Count their planned losses together and describe that common exposure. Historical correlation can change; a correlation estimate is not a loss cap. Beginners can simplify this by holding one demo position at a time.

Practice

Calculate the size for a 10 USD budget, EUR/USD 20 pip executable stop distance, 10 USD per pip per standard lot, 7 USD commission per lot, and a 2 pip slippage allowance. The size increment is 0.01 lots. Show the estimate after rounding. Then explain the shared exposure of long EUR/USD and long GBP/USD.

Check your understanding

After the four lessons in this module, complete Module 2 knowledge check from the course overview. It contains the three questions from each lesson with feedback after submission. Keep written calculations in your workbook.

Glossary

Commission: A separate trading charge under the provider’s terms
Correlation: A statistical description of how variables move together in a sample
Equity: Account value including open profit or loss and applicable adjustments
Long: Exposure that benefits from a higher pair price before costs
Lot: A position volume convention; verify base units for the instrument
Pip: A conventional exchange rate movement unit
Short: Exposure that benefits from a lower pair price before costs
Slippage: Difference between a reference price and the actual execution fill
Spread: Ask minus bid