Compound vs fixed lot — which position sizing system?

For a hypothetical account starting at EUR25,000, a 10% gain gives EUR27,500. Ten subsequent losses of 2% of current equity leave EUR27,500 x 0.98^10 = EUR22,469.50, before costs. With unchanged stop distance and pip value, volume decreases during that loss sequence; it is not larger than at the original start on every trade.

What actually separates compound sizing from a fixed lot

Sizing determines exposure for an entry and exit rule. Compare it using the full payoff sequence, costs, cash flows and instrument constraints. Win rate and average win/loss alone do not determine the account’s path or validate its next five years.

Fixed-fractional sizing sets a modeled cash-loss budget as a fraction of the stated capital base. Ignoring costs and slippage, lots = (capital × fraction) / (stop pips × account-currency pip value per lot). For a hypothetical EUR 10,000 account, assume EUR/USD conversion of 1.0000 USD per EUR, 100,000 EUR per lot, a 30-pip exact exit and 0.01-lot steps. Then EUR 10 per pip per lot and a chosen 1% budget yield 0.3333 lot, rounded down to 0.33 (EUR 99 planned price loss). EUR 12,000 and EUR 15,000 yield 0.40 and 0.50 lot. Changing the stop or conversion changes volume even at unchanged capital.

A fixed lot is the opposite. You trade 0.1 lot whether the balance shows €10,000, €12,000 or has fallen after a drawdown to €5,000. Position size is insulated from the equity curve, and that insulation is the source of both its strengths and its limitations.

What does the math of the two systems look like?

For an arithmetic comparison only, assume a hypothetical net gain of 12% at each year-end with no intervening cash flows. The compounded model multiplies each year’s balance by 1.12. A separate fixed-cash model adds EUR 1,200 each year. These stipulated annual paths are not forecasts or consequences that follow automatically from fixed-percentage and fixed-lot trade sizing.

The five-year difference is EUR 1,623.42, about 10.15% of the fixed-cash result (or 16.23% of starting capital). At ten years it is EUR 9,058.48, about 41.17% of the fixed-cash result. These conclusions follow from the stipulated annual paths. They do not establish a general advantage of percentage-based trade sizing or require a claim about how often drawdowns occur.

Why drawdowns hurt more than the formula implies

Recovery is asymmetric: a decline d requires growth d/(1 − d) from the remainder. Thus 20%, 30%, 50% and 80% declines require 25%, about 42.86%, 100% and 400% respectively. If growth were continuously equivalent to 12% yearly, recovery from 30% takes ln(1/0.7)/ln(1.12) ≈ 3.15 years; from 50%, about 6.12 years. With gains credited only at year-end, the first recovering year-ends are year 4 and year 7. No recovery rate is assured.

The proportional recovery calculation applies to either sizing method. With the same chosen fraction, a lower capital base reduces the next modeled cash budget. Fixed volume can instead keep a given price-loss amount unchanged only if stop distance and instrument value are unchanged. Neither rule guarantees recovery or removes execution constraints.

In a hypothetical fixed-fractional model, equity grows from EUR 10,000 to EUR 20,000, then falls 20% to EUR 16,000. If stop distance and EUR pip value stay fixed, volume scales from 0.10 to 0.20 and then 0.16 lot. The modeled cash loss at EUR 16,000 is 1.6 times the starting amount, not twice; at the EUR 20,000 peak it was twice.

• Cash amounts and percentages differ. A hypothetical 10% decline is EUR 5,000 on EUR 50,000 and EUR 500 on EUR 5,000. These amounts alone do not determine which drawdown the trader can tolerate.
• Recovery requires a stated payoff rule. A 10% decline requires about 11.11% growth from the remainder. Whether recovery is faster in cash under fixed volume depends on the future entries, exits, conversion and costs.
• Sample history is not certainty. Record how a rule was evaluated and the uncertainty of its estimated payoff distribution. A long profitable sample does not guarantee future expectancy or a calm response to losses.

A hypothetical hybrid — percentage sizing with volume bounds

A percentage-based formula can be combined with an imposed volume floor or ceiling. This is an additional constraint, not the definition of anti-martingale or proof of a common industry practice. Examine how it changes planned risk when capital falls.

For this hypothetical hybrid, calculate percentage-based volume, then apply a self-imposed floor of 0.10 lot and ceiling of 1.00 lot. The floor may force volume above the budget; the ceiling may leave some budget unused. These are experiment parameters, distinct from the provider’s minimum and step.

Assume unchanged stop distance and conversion, and a formula giving 0.10 lot at EUR 10,000. EUR 15,000 gives 0.15 lot, while EUR 5,000 gives 0.05 before the imposed 0.10 floor. The floor doubles modeled loss relative to that calculation. At EUR 100,000 the formula reaches 1.00 lot; only above that capital does the ceiling constrain it. This is a hypothetical rule, not a recovery recommendation.

A lot floor can keep volume above a percentage-based calculation after losses, thereby increasing the modeled risk percentage. It does not guarantee faster recovery or prevent paralysis. If minimum tradable volume exceeds a chosen loss budget, the trade does not fit that budget; a smaller permitted instrument or no trade may be necessary. A drawdown review rule does not guarantee a fill-price cap.

The step-up system — a discrete alternative

A separate hypothetical design uses capital bands to change the chosen fraction. Define the exact boundaries, any drawdown override and the order in which conditions are applied. These settings are not proven standards and alter more than volume rounding.

Predetermined bands make the rule traceable, but do not eliminate fear, overconfidence or execution losses. Test boundary effects: crossing a threshold can raise the chosen fraction abruptly, even when capital changes only slightly. A review trigger is a decision rule, not a guaranteed circuit breaker.

A hypothetical trade-level comparison

In a hypothetical binary model, let each trade win +2R with probability 0.4 and lose -1R with probability 0.6. Expected payoff is 0.4 x 2 - 0.6 = 0.2R. Over 200 such trades the arithmetic expected sum is 40R, not a guaranteed realized result.

For a hypothetical EUR 10,000 account, assume EUR/USD conversion stays at 1.0000 USD per EUR. At 0.10 lot, a 30-pip exact stop fill then gives a modeled EUR 30 loss, or 0.3% of starting capital, before costs. A constructed year with 80 wins at +2R and 120 losses at −1R, all using fixed EUR 30 R, gives EUR 1,200. The annual fixed-cash table stipulates that amount each year; neither sizing nor the sample win rate guarantees it.

The table compares stipulated annual paths: 12% growth at each year-end gives EUR 11,200, then EUR 12,544, and about EUR 17,623 after five years. Trade-level compounding is a different calculation. With exactly 80 wins at +2R, 120 losses at −1R and risk fixed at 0.3% of current equity, the ideal cost-free factor is 1.006⁸⁰ × 0.997¹²⁰, or about 12.53% growth. In that specific model, counts determine the final factor, while order determines the intervening drawdown.

In the constructed year-three example, a 30% decline leaves the compounded annual-path model at EUR 8,780.80 and fixed-cash model at EUR 8,680. If subsequent growth were 12% yearly, either would need about 3.15 years to recover proportionally. If the fixed-cash model instead adds EUR 1,200 yearly, replacing its EUR 3,720 loss takes 3.1 years. Keep each stipulated recovery rule explicit; no rate is assured.

What to choose at your stage

Compare methods against the same planned loss budget and constraints. Experience alone does not determine suitability; a fixed lot can be too large, and percentage sizing can still exceed its modeled budget at an actual fill.

No universal live-trading timetable, lot size or sample count makes a sizing method appropriate. Compare planned price loss and costs with current capital and total exposure, check minimum volume and stress gaps. Neither 200 trades nor two profitable years guarantees an edge, and a volume floor can increase percentage risk after losses.

Common mistakes in choosing position size

1. Ignoring the loss path. Stress a specified sequence with costs and volume limits. The formula’s proportional budget does not prove that drawdown will remain tolerable.
2. Unrecorded sizing changes. Distinguish a change caused by stop distance or conversion from an override of the selected rule. Both require explicit inputs to reconstruct the path.
3. Confusing conditional losses with probabilities. Ten exact losses at 5% of current capital give 40.13% drawdown, versus 18.29% at 2%, before costs. These calculations do not establish how likely that streak is or a universally appropriate fraction.
4. A volume floor that exceeds the budget. As capital falls, a minimum lot can imply more percentage risk than planned. Do not round volume upward merely to preserve a recovery target; compare the minimum with the full modeled loss budget and instrument constraints.
5. Leaving exposure constraints undefined. Check notional, margin, total open risk and available volume, as well as the per-trade budget. A ceiling does not guarantee emotional comfort or a maximum execution loss.

Conclusions — which system for whom

Under the stipulated annual paths, EUR 10,000 becomes about EUR 17,623 after five 12% compounded gains and EUR 31,058 after ten; adding EUR 1,200 yearly gives EUR 16,000 and EUR 22,000. Trade-level percentage sizing and fixed lots do not automatically generate those annual paths. Compare complete sequences rather than presenting the arithmetic as a measured strategy edge.

Select a sizing rule from the monetary risk budget, stop distance, account-currency pip value and available volume step. Account age or 200 completed trades does not by itself validate a strategy or a sizing floor. Any lower volume floor can breach a percentage budget after losses; reduce exposure or skip the trade when the feasible minimum is too large.

What to do tomorrow

1. Calculate planned risk in account currency. Multiply stop distance by pip value per lot and the actual number of lots, then divide by equity at entry. Add applicable costs and record possible slippage separately. Different percentages can reflect changing inputs or explicit rules, not necessarily mood.
2. Write the sizing rule and its limits. State the planned risk percentage, volume step and maximum exposure. A broker's minimum trade volume is a feasibility constraint: if it exceeds the risk budget, skip the trade rather than force a floor above the calculated size.
3. Define a drawdown review rule. Write the chosen threshold, action and conditions for resuming the evaluated rule. A week off, a particular sample count or returning to fixed lots does not by itself make future trading safe.

Related reading: position size and the 1 percent rule — the fundamentals of risk per trade; maximum drawdown explained — the mathematical trap of losing streaks; 2% vs 1% risk rule — when and how to scale up risk per trade.