Account balance ($)
Risk per trade (%)
Stop loss (pips/points)
Symbol
Scaling method
Consecutive wins (for scaling)
Full breakdown (click to copy)
Trading Decision
Check the Safety card first
If it reads "Unsafe," the chosen scaling method has pushed your real risk well past the risk % you entered — this is a warning to stop and reconsider, not a number to trade as-is.
Martingale needs a hard limit you set yourself
This calculator won't stop you from entering a large losing streak, but the position size grows exponentially as it tries to recover — decide your own maximum consecutive-loss cutoff before you start, not after you're several trades deep.
"Conservative" isn't the same as "optimal"
The Conservative method here is a flat 0.5× multiplier, not a formula derived from your actual edge. If you know your win rate and R:R, a true Kelly-based size will differ from this estimate.
➜ Next step: For a position size derived from your actual win rate and risk:reward — not a flat multiplier — use the Kelly Criterion Calculator. If you're tracking real trading results, verify your edge is genuine first with the Win Rate & Expectancy Calculator.
How to Use the Position Scaling Calculator
- Enter account balance — your current total account equity.
- Set risk per trade % — the percentage of account you want to risk. Start at 1% for prop firm accounts, 0.5% for challenge phase.
- Enter stop loss in pips — the distance from entry to stop loss for your specific trade setup. This is the key variable — it changes with every trade.
- Select your instrument — choose from XAUUSD (Gold), major forex pairs, NAS100, or SPX500. Each has a different pip value per lot.
- Choose scaling method — Fixed Fractional for consistent risk, Anti-Martingale to scale up during winning streaks, or Conservative for a flat half-size position.
- Review the comparison table — the calculator shows position sizes at different risk percentages, letting you instantly compare the dollar risk and lot size at 0.5%, 1%, 2%, and 3%.
⚠️ Prop firm rule: Always calculate position size AFTER setting your stop loss, not before. Never set a stop loss to fit a predetermined lot size — this is reverse risk management and leads to stops that are too tight or too wide for the actual market structure.
Understanding Position Scaling Methods
📊 Fixed Fractional
Risk the same percentage of account on every trade. As balance grows, position size grows proportionally. As balance shrinks, position size shrinks — protecting capital during drawdowns. The gold standard for consistent traders.
📐 Conservative (0.5×)
A flat half-size version of your fixed-fractional position — not a Kelly calculation. It doesn't use your win rate or R:R, so it's a simple, predictable way to trade smaller, not an edge-based optimal size. For that, use the dedicated Kelly Criterion Calculator, which does require knowing your true win rate.
📈 Anti-Martingale
Increase position size after winning trades, decrease after losers. Capitalises on winning streaks, protects capital during losing streaks. Popular with trend traders who experience momentum clustering.
📉 Linear Scaling
Increase position size gradually as balance grows, following a predetermined schedule. Less dynamic than other methods but simple to implement and explain to prop firms.
🚨 Martingale (Avoid)
Doubles position size after every loss. Mathematically guaranteed to eventually cause account ruin. Absolutely prohibited by most prop firms and lethal in any account with a drawdown limit.
For prop firm trading, Fixed Fractional at 0.5–1% risk per trade is almost universally the correct choice. The other methods have their place in personal trading where no external drawdown limits apply, but the strict daily and maximum drawdown rules of prop firms make any variable-size method risky.
Advanced Position Sizing Concepts
The stop loss determines everything
At 1% risk on a $100K account, your risk amount is $1,000. A 10-pip stop on EURUSD ($10/pip/lot) allows 10 lots. A 50-pip stop allows only 2 lots. The wider your stop, the smaller your position — this is mathematically forced, not a choice. Traders who use tight stops to enable larger lots are taking more structural risk, not the same risk.
Scaling during drawdown
Many professional traders reduce their risk percentage during drawdown periods. If the account drops 3% below peak, reduce from 1% to 0.75% risk. At 5% below peak, reduce to 0.5%. This slows the drawdown compounding effect and preserves capital during losing streaks while keeping you in the market.
Position sizing for correlation
If you trade multiple correlated pairs simultaneously (e.g. EURUSD and GBPUSD, which have 0.89 correlation), your actual exposure is much higher than your per-trade risk suggests. When running correlated trades, halve your position size on each to maintain your intended total risk exposure.
🔢 The rule of thumb: Never risk more than 1% on a single trade in a prop firm challenge. Never have more than 2% total open risk at any time. These two rules alone prevent the majority of challenge failures caused by position sizing errors.
Position Scaling Formula
Base Position = (Balance × Risk %) ÷ (Stop Loss × Pip Value per Lot), then adjusted by the chosen scaling method's multiplier.
Fixed Fractional
Base position, unchanged — the same risk % on every trade regardless of streak.
Martingale
Base × 2^(consecutive losses) — doubles size after every loss, attempting to recover prior losses with the next win. Grows exponentially and has no built-in ceiling.
Anti-Martingale / Linear
Base × (1 + streak × 0.5) or × (1 + streak × 0.25) — grow more gently on winning streaks, scaling back down automatically once the streak ends.
Worked example
$10,000 balance, 1% risk, 20-pip stop on XAUUSD ($10/pip/lot): base position = $100 ÷ (20 × 10) = 0.5 lots. With Fixed Fractional this stays 0.5 lots on every trade. With Martingale after 3 straight losses: 0.5 × 2³ = 4 lots, sized up to try to recover the prior losses with one win — 8% actual risk on that single trade, already flagged Unsafe by this calculator's built-in check.
Avoid These Mistakes
Trusting martingale because the math "checks out"
Doubling after every loss is mathematically consistent as a recovery scheme, but a handful of losses in a row compounds a small starting position into an account-threatening one. Correct math doesn't mean safe sizing — this is precisely why martingale is infamous.
Treating "Conservative" as a true Kelly size
This method is a flat half-size multiplier, not an edge-based calculation. Don't quote it as "my Kelly size" — use the dedicated Kelly Criterion Calculator if you need the real formula.
Setting the stop loss to fit a lot size
Reverse risk management — deciding the position size first and shrinking the stop to match produces stops too tight for real market structure.
Ignoring correlated positions
Running this calculator per-trade without accounting for other open, correlated positions understates your real total exposure.
Frequently Asked Questions
What is fixed fractional position sizing?
Fixed fractional means risking the same percentage of your account on every trade (e.g. 1%). As your account grows, your position size grows proportionally. As it shrinks, your size reduces. This is the safest and most recommended method for consistent long-term growth.
Does the "Conservative" method use the Kelly Criterion?
No. The Kelly Criterion is a formula that calculates optimal bet size from your actual win rate and risk:reward (Kelly % = Win Rate − (Loss Rate ÷ RR)), typically halved in practice for lower variance. This calculator's Conservative method is simply half of your fixed-fractional position size — it doesn't take win rate or R:R as inputs, so it isn't a Kelly calculation. For a real edge-based size, use the dedicated Kelly Criterion Calculator.
What is anti-martingale scaling?
Anti-martingale increases position size after winning trades and decreases after losing trades — the opposite of martingale. This lets you capitalise on winning streaks while protecting capital during losing streaks. It's much safer than martingale and used by many professional traders.
Is martingale safe for prop firms?
No. This calculator's Martingale option doubles your position size after each consecutive loss, attempting to recover prior losses with the next win — this compounds into an extremely large position after just a handful of losses, and this calculator flags it as Unsafe once actual risk passes 3× your intended risk %. Most prop firms explicitly prohibit or heavily discourage aggressive recovery strategies like this. Use fixed fractional instead.
References
🏛️ U.S. NFA
Position sizing and risk-disclosure guidance for retail trading — nfa.futures.org
🇪🇺 ESMA
EU retail risk-management framework — esma.europa.eu
📄 Prop firm rulebook
Maximum position size, daily loss, and prohibited-strategy rules vary by firm — always confirm against your own challenge's published rules before scaling up.
Last updated: 12 July 2026 · The "Unsafe" threshold flags actual risk above 3× your stated risk % — a general caution signal, not a substitute for your prop firm's specific rules.