Skip to content
CyclepediaThe trading encyclopedia
ITENESPT-BRFRDE
Learning path Silver Repeatable method

Position sizing

A method for converting a risk budget and stop distance into tradable quantity, including point value, costs, rounding and portfolio constraints.

On this page

Who it is for — Readers choosing how many shares, units, lots or contracts to trade without letting available leverage decide their risk.

Position sizing converts a risk-per-trade budget and an invalidation distance into a tradable quantity. The formula is a starting point: minimum lot, liquidity, margin, leverage and total exposure can impose a lower operational quantity.

In simple terms — The stop level determines what one unit would cost if the idea fails. The budget determines how many units the account can support. Size comes last.

From risk budget to tradable quantity Position sizing is a chain of testable assumptions, not a shortcut. Linear example: €500 budget · €20 fixed costs · 30 ticks × €10 · theoretical quantity 1.6 → tradable 1 From risk budget to tradable quantity Position sizing is a chain of testable assumptions, not a shortcut 1 Risk budget B €500 Planned loss budget, not aguaranteed maximum loss. ↗ Cyclepedia 2 Unit risk 30 × €10 |E−S| × point value × FXconversion + variable costs. ↗ Cyclepedia 3 Theoretical quantity 480 / 300 = 1.6 (Budget − fixed costs) / riskper unit. ● 4 Tradable quantity 1 contract Round down; then check margin,leverage, liquidity and totalexposure. ↗ Cyclepedia Linear example: €500 budget · €20 fixed costs · 30 ticks × €10 · theoretical quantity 1.6 → tradable 1
Select a stage to open its detail. The calculation includes point value, costs and rounding; on narrow screens, the figure scrolls horizontally.

General formula

In simple terms — Distance in points is not enough. It must be converted into the account currency using the instrument’s point or tick value.

Let:

  • B be the monetary risk budget;
  • C_f be estimated fixed transaction costs;
  • E be the entry price;
  • S be the stop;
  • V be the monetary value of one point per unit or contract;
  • F be the conversion factor into the account currency;
  • C_u be variable costs and estimated slippage per unit.

Estimated risk per unit is:

Unit risk = |E − S| × V × F + C_u

and theoretical quantity is:

Theoretical quantity = (B − C_f) / unit risk

Operational quantity should be rounded down to the tradable increment:

Quantity = floor(theoretical quantity / minimum lot) × minimum lot
Instrument What to use for V
Shares in the account currency Usually 1 per price unit and share
Futures Contract multiplier or tick value
Foreign exchange / CFDs Pip or point value per lot and currency conversion
Options or another nonlinear/inverse instrument Strategy payoff, sensitivities and scenario analysis; the linear formula may not apply

Example — €500 budget, €20 estimated fixed costs, a stop 30 ticks away, and a tick value of €10, with variable costs already included in the buffer. One contract carries €300 of price risk. (500 − 20) / 300 = 1.6, so size is 1 contract. Two contracts would create €600 of price risk before costs, above the budget.

Operating sequence

In simple terms — The calculation is only as valid as its inputs: a reasoned stop, correct contract specifications and known aggregate risk.

  1. Define invalidation. The technical stop comes from the hypothesis, not the desired size.
  2. Set the budget. In money or as a percentage of capital, considering other positions as well.
  3. Read the specifications. Tick size, tick value, multiplier, settlement currency and minimum lot.
  4. Calculate and round. Always down relative to the stated budget.
  5. Apply constraints. Margin, leverage, exposure, liquidity and broker or exchange rules.
  6. Estimate execution. Spread, commissions, slippage and gap risk.

Volatility and the stop

Higher volatility may require a wider stop when invalidation must remain beyond ordinary noise. With the same budget, a wider distance means a smaller size. Average True Range can be one input, but it does not determine either the stop or the risk on its own.

Stop distance Risk per unit Effect on size, fixed budget
2 points 2 × V Larger
4 points 4 × V Halved

Common mistake — Using the same lot size with different stops. If distance rises from 5 to 50 points while everything else remains equal, price risk increases tenfold.

Controls the formula does not replace

A quantity derived from one trade can still be excessive:

  • correlated positions can lose together;
  • size can exceed allocated capital or a leverage limit;
  • an order large relative to available depth can increase slippage;
  • margin requirements can change and force reductions;
  • a stop can execute beyond the expected price, while a stop-limit may remain unfilled.

For options, the simple entry-to-stop distance does not always describe the risk. Value and sensitivity change with the underlying price, volatility and time; some short option positions can lose far more than the premium received. Scenario analysis should match the strategy payoff.

There is no universal risk percentage. Teaching examples such as 1% or 2% are not rules: the choice depends on the strategy, loss distribution, leverage, objectives and tolerance for drawdown.

Pre-order checklist

  • Inputs: are budget, stop, tick/point value and currency verified?
  • Rounding: has quantity been reduced to a tradable increment?
  • Portfolio: do aggregate risk and correlation remain within the plan?
  • Execution: are costs and possible slippage included?

Silver path — Planning and management module. Index: Silver path.

Sources

  • CME Group, Proper Position Size — stop → budget → contracts process, using tick distance and tick value.
  • U.S. Securities and Exchange Commission, Investor.gov, Trading Basics, pp. 2–3 — differences between stop and stop-limit orders and the risk that trigger and execution prices diverge.
  • U.S. Securities and Exchange Commission, Investor.gov, An Introduction to Options — nonlinear payoffs and risks specific to option buyers and sellers.
Suggest an edit My proposals