Glossary

Position sizing for prop firm challenges

Last reviewed: 16 September 2026·Tradelyze

Position sizing is choosing how many contracts, shares or lots to trade so that a strategy's worst realistic loss fits inside a limit you cannot break. For a prop firm challenge, divide each dollar limit by the matching one-contract loss from your backtest, take the smallest answer and round down.

New to this? Start with prop firm rules and backtest metrics.

Why does position size decide whether a strategy breaks a prop firm drawdown rule?

Position size decides whether a strategy breaks a prop firm drawdown rule because the rule allows a fixed number of dollars, while the strategy's losses grow with every contract you add. A drawdown rule limits how far the account may fall, and the amount it allows is called the drawdown allowance. Adding contracts does not change when the strategy enters, when it exits or how often it wins. It multiplies every dollar it loses.

Take one strategy traded on one Micro E-mini Nasdaq-100 (MNQ) futures contract. Constructed illustration, not measured data. Its worst day loses $190, and its deepest fall from a high is $340. On five contracts, the same trades lose $950 on the worst day and fall $1,700 from a high. Against a $1,500 allowance, the one-contract version fits and the five-contract version fails, with identical entries, exits and win rate.

The prop firm rules page makes the same point in its table of which backtest statistic predicts which rule: limits are fixed amounts, and losses scale with size. So when a drawdown rule fails, test a smaller size before you rewrite the strategy. The maximum drawdown page explains why a drawdown figure says as much about the size traded as about the strategy.

How do you convert a prop firm's percentage limit into dollars?

To convert a prop firm's percentage limit into dollars, multiply the percentage by the account size the firm names, which is usually the balance you started with, not your current balance. FTMO's Trading Objectives page, retrieved 16 September 2026, states its limits as percentages of the Initial Simulated Capital. A 5% Maximum Daily Loss on a $100,000 account is therefore $5,000, and it stays $5,000 after the account grows. Topstep's Maximum Loss Limit article, retrieved the same day, skips the conversion and states the limit in dollars.

The $100,000 FTMO rows are arithmetic on FTMO's percentages, so the dollars scale with whichever account size you buy. Two details change the room you actually have. A trailing allowance is measured from the account's high point. After a good week, the room left is the allowance minus what you have given back since that high; trailing drawdown walks through it. A daily allowance starts again each day, and at FTMO it stays a fixed dollar amount; daily loss limit covers reset times and open losses.

Tradelyze measures every prop firm percentage against the account size the run trades, which it reads from the initial_capital argument of your script's strategy() declaration. Set that argument to the size of the account you intend to buy, or every percentage in the report describes a different account.

How do point value and tick size turn a price move into dollars at risk?

Point value and tick size turn a price move into dollars at risk by fixing what each unit of movement is worth. Point value is the number of dollars one futures contract gains or loses when price moves one full point. Tick size is the smallest step price can move, and the tick value is tick size times point value. The same stop distance can be worth $80 on one contract and $800 on another.

Worked example, constructed illustration, not measured data: a 40-point stop is 160 ticks of 0.25. By the lookup table's point values, it risks 40 × $2 = $80 on one MNQ contract and 40 × $20 = $800 on one NQ contract. A micro contract carries one-tenth of the E-mini's point value. A strategy too large for an allowance on one E-mini can often be traded in micros instead, where each E-mini's risk splits into ten smaller steps.

On a forex account the same arithmetic runs through the lot. The platform's symbol specification states how many units of currency one lot is. Units times the pip size gives the pip value, converted to the account currency. For a lot of 100,000 units of EUR/USD on a US dollar account, a pip of 0.0001 is worth $10, so a 25-pip stop on 0.5 lots risks $125. The platform's own specification overrides this example.

In Tradelyze, Point Value and Tick Size are filled from the lookup table on the Basic Info step. A wrong point value scales every dollar drawdown in the report; see what point value and tick size are.

How much should you risk per trade in a prop firm challenge?

How much to risk per trade in a prop firm challenge has no single sourced answer: no primary source establishes one correct percentage of the account, so this page gives none. Risk per trade is the dollars a trade loses if it reaches its stop, which is the stop distance in points times point value times contracts, plus costs. What the allowance does settle is how many full losses in a row the account can take before the rule ends it.

Constructed illustration, not measured data: 10 full losses of $150 in a row from a high use up a $1,500 trailing allowance, and so do 5 losses of $300. Under a $600 daily loss limit, the fourth $150 loss in one day reaches the limit. Firms fail an account that touches its limit, so the account survives one loss fewer than the division suggests. Stops can fill worse than their price in a fast market or across a gap, so the real loss on a stopped trade can be larger than the planned risk.

Compare the count with the longest losing streak in your backtest, then with a Monte Carlo view, because a backtest shows only one order in which the trades could have arrived. A strategy without a fixed stop has no risk per trade to divide by. Size that kind of strategy from its backtest drawdowns, as the next section describes.

Which backtest number should you size from: worst day, maximum intraday drawdown or Monte Carlo 95th-percentile drawdown?

Size each prop firm rule from the backtest number that measures the same thing the rule measures. For a daily loss limit, that is the worst single day. For a total or trailing limit, it is the deeper of the maximum intraday drawdown and the Monte Carlo 95th-percentile drawdown. Maximum intraday drawdown is the largest fall from a running high to a later low, with open trades valued as price moved. The 95th-percentile drawdown is the fall that 95 of every 100 reshuffled orderings of your trades stayed within.

The backtest's own maximum drawdown comes from the one order in which the trades happened to arrive. A Monte Carlo simulation reshuffles the same trades into many orders and reports how deep the fall gets across them; sizing off the Monte Carlo drawdown explains why that is the better base. The 95th percentile is not a worst case, since 1 run in 20 fell further. Any extra margin on top is a judgment call, and this page found no primary source for a standard safety factor. The share of runs that broke the limit is an estimate of risk of ruin, which answers how often rather than how deep.

How many contracts fit a $1,500 trailing drawdown allowance?

In the example below, two MNQ contracts fit a $1,500 trailing drawdown allowance and three do not, even though the real-order drawdown alone would seem to allow four. Constructed illustration, not measured data. The account is $30,000, with a $1,500 end-of-day trailing allowance and a $600 daily loss limit. The strategy's backtest on one MNQ contract shows a worst day of $190, a maximum drawdown of $340 in its real trade order and a Monte Carlo 95th-percentile drawdown of $520.

1. Daily limit: $600 ÷ $190 = 3.16, rounded down to 3 contracts.
2. Trailing allowance on the real-order drawdown: $1,500 ÷ $340 = 4.41, rounded down to 4 contracts.
3. Trailing allowance on the 95th-percentile drawdown: $1,500 ÷ $520 = 2.88, rounded down to 2 contracts.
4. Result: the smaller of the daily answer (3) and the 95th-percentile answer (2) is 2 contracts.

Two contracts leave $460 of room at the 95th percentile, only a little more than one worst day ($380) at that size. Sizing from the real-order drawdown alone would have picked four contracts, and four contracts break the $600 daily limit on the strategy's own worst day. The table's per-contract multiplication also assumes that costs and fills scale evenly with size, which the next section tests.

Why doesn't a one-contract backtest scale up exactly?

A one-contract backtest scales up exactly only when every cost is charged per contract and every extra contract fills at the same price. Three things break that assumption: costs that are not charged per contract, the smallest size you can actually trade, and sizing by a percentage of equity. Each one makes the simple multiplication from the previous section wrong by an amount the one-contract figures cannot show.

Which costs do not grow with the number of contracts?

TradingView's Help Center page on strategy properties, retrieved 15 September 2026, lists commission types that include a percentage of the transacted value and currency per contract, and both of those grow with size. A fee charged per order, or a monthly platform or data charge, does not. Slippage, which TradingView describes as a value in ticks added to the fill price of market or stop orders, is a fixed figure in the backtest. A larger order in a thin market can fill further from the price than a small one, and a fixed tick figure cannot show that. TradingView strategy properties explains each cost setting.

What happens when the answer is 2.88 contracts?

You trade 2. Futures trade in whole contracts, so the arithmetic always rounds down, and the size you can hold moves in steps: going from 2 contracts to 3 adds 50% more risk at once. Micro contracts make the steps smaller. By the point values in Tradelyze's futures lookup table, one MNQ contract carries one-tenth of the dollar risk of one NQ contract.

Why does percent-of-equity sizing compound?

TradingView's strategy properties page says a percentage-of-equity order is sized as a percentage of the available equity when the trade opens. After a run of wins the positions are larger, so a later losing streak costs more dollars than the same streak did early on. Such a backtest has no fixed contract count to scale. The same page puts the default initial capital at 1,000,000, so a script that never sets initial_capital sizes those percentages from an account far larger than a challenge. A prop firm allowance is a fixed number of dollars, and a fixed contract size keeps each loss tied to it.

How do you change position size in a Pine Script strategy before resubmitting it?

To change position size in a Pine Script strategy, edit the default_qty_type and default_qty_value arguments of its strategy() declaration, and set initial_capital to the account size. TradingView's Help Center page on strategy properties, retrieved 15 September 2026, says each property can be changed by editing the arguments of the strategy() call. It lists three order-size types: strategy.fixed for a number of contracts, shares or lots, strategy.cash for an amount of currency, and strategy.percent_of_equity for a percentage of equity.

The declaration above is a constructed example: it trades 2 contracts on a $30,000 account, and its commission figure is a placeholder for your broker's real charge. Tradelyze runs your strategy with the values written in the script, not with changes made in TradingView's Properties tab. A size set only in that tab never reaches the run; why script defaults must match covers the details.

1. Change default_qty_value, and initial_capital if needed, in the script and save it.
2. Apply the saved script to the chart in TradingView and let the Strategy Tester run again.
3. Export the new trade list, so the trades you upload were made at the new size.
4. Submit the edited script, the new trade list and the price data to Tradelyze as a new strategy, then read the drawdown rows and MC Max DD Real→P95 at the new size.

Why does a smaller position size make a prop firm evaluation take longer?

A smaller position size makes a prop firm evaluation take longer because the profit target is a fixed dollar amount, while the profit per day shrinks with every contract you remove. FTMO's Trading Objectives page, retrieved 16 September 2026, sets a 10% Profit Target on the FTMO Challenge phase of the 2-Step Challenge and on the 1-Step Challenge, measured on the Initial Simulated Capital. A $100,000 account needs $10,000 of profit whatever size you trade.

Constructed illustration, not measured data: a $30,000 account with a 10% target needs $3,000 of profit. A strategy that averages $60 of profit per trading day on one contract needs about 50 trading days on one contract, 25 on two and 17 on three. Averages hide losing stretches, so the real time varies around those figures.

Two other rules do not move with size. A minimum-trading-days rule counts days, so FTMO's requirement of at least 4 Trading Days on the 2-Step Challenge is the same at any size. A consistency rule compares the best day with total profit; FTMO's 1-Step Best Day Rule requires the Best Day to be no more than 50% of Positive Days' Profit. Trading more or fewer fixed contracts scales every day by the same factor, so that share does not change. The trade-off is time: every extra day of the evaluation is another day a drawdown rule can be hit. What a consistency rule's best-day cap does covers the rule itself.

Where does Tradelyze show the numbers you need to size a strategy?

Tradelyze shows the numbers you need to size a strategy in two places: each selected firm's Rule Results table and the MC Max DD Real→P95 row of the robustness card. Both come from the trades your script produced at the size written in its strategy() declaration, so they describe that size and no other.

• Rule Results table. Each row shows a Status mark, the Rule, the Actual value your backtest reached, the Limit and a Message. The daily drawdown row gives the worst day as a percentage of the starting account size by default. The total drawdown row uses the rule set's drawdown type: Static, EOD Balance, Trailing Realtime or Trailing EOD. Multiply a percentage by initial_capital to get dollars. How to read the Rule Results table covers every column.
• MC Max DD Real→P95. The first number is the maximum drawdown of your trades in their real order, and the second is the 95th percentile of the simulated drawdowns. Both are percentages of the running peak, not of the starting balance, so multiplying them by the starting balance gives a dollar figure at or below the true fall.
• Ruin Probability. The share of simulated runs whose drawdown went past the selected firm's total drawdown limit. Tradelyze needs it below 20% for the Monte Carlo check to pass, and leaves it blank when the rule set has no total drawdown limit. Ruin Probability and MC Max DD Real→P95 explains both figures.

Because both drawdown rows are percentages of the same starting account size, a fixed-size strategy can be rescaled on paper. Constructed illustration, not measured data: a script trading 3 MNQ contracts with initial_capital=30000 shows a total drawdown Actual of 6.3% against a Limit of 5%. That is $1,890, or $630 per contract, so the $1,500 allowance fits 2 contracts, a $1,260 drawdown. Edit the script to 2 contracts and submit it again, because costs and the Monte Carlo figures need a real run.

A Not Feasible badge with a failing drawdown row is the case this page is for. Tradelyze does not check time limits, news trading or weekend holding; what Qualifies and Not Feasible mean covers what the badge does and does not include. Firm presets record rules as they were understood when written, so check the limits against the firm's current terms. Account and credit questions are answered in the Learn FAQ.

Frequently asked questions about position sizing for prop firm challenges

Sources

• FTMO, Trading Objectives, ftmo.com/en/trading-objectives, retrieved 16 September 2026 — 2-Step Challenge: Profit Target 10% in the FTMO Challenge phase and 5% in Verification; Maximum Daily Loss 5% of the Initial Simulated Capital, recalculated daily at 00:00 CE(S)T; static Maximum Loss 10%; at least 4 Trading Days. 1-Step Challenge: Profit Target 10%; Maximum Daily Loss 3%; end-of-day trailing Maximum Loss 10% that can only increase; Best Day Rule of no more than 50% of Positive Days' Profit.
• Topstep, What is the Maximum Loss Limit?, help.topstep.com article 8284204, retrieved 16 September 2026 — Maximum Loss Limit of $2,000 on a 50K account, $3,000 on 100K and $4,500 on 150K; “The MLL is a trailing limit. It rises as your end-of-day balance grows, but never moves down. Once it reaches your starting balance, it locks permanently.”; realized and unrealized P&L both count, and the limit is monitored in real time. The article prints no calendar date in its visible text; its page metadata gives a last-modified date of 2 September 2026.
• TradingView Help Center, Strategy properties, tradingview.com/support/solutions/43000628599, retrieved 15 September 2026 — order size as Quantity (strategy.fixed), Amount in currency (strategy.cash) or Percentage of equity (strategy.percent_of_equity), the last “calculated as a percentage of the available equity when the trade opens”; initial capital “By default, this value is equal to 1,000,000”; commission as a percentage of the transacted value or currency per contract; slippage in ticks; and that each property “can be changed by editing the arguments of the strategy() function call”.
• Tradelyze implementation, reviewed 15 September 2026 — every prop firm drawdown percentage is measured against the initial_capital in the script's strategy() declaration; the daily drawdown basis defaults to the starting account size; the Rule Results table columns Status, Rule, Actual, Limit and Message; the four drawdown types; MC Max DD Real→P95 as a percentage of the running peak; Ruin Probability counted against the selected firm's total drawdown limit, below 20% to pass the Monte Carlo check and blank without such a limit; runs use the script's own defaults; point values and tick sizes from the futures lookup table, which should be checked against CME Group's published contract specifications.
• Constructed illustrations — every account, strategy, trade and commission figure in this page's worked examples, tables and Figure 1 is constructed, not measured data.