Futures Position Sizing: How Many Contracts Should You Trade?

Position sizing is the only part of trading where the right answer is arithmetic. You do not have to predict anything to get it right, and getting it wrong is what ends most funded accounts, usually while the strategy underneath was working perfectly well.

This is the calculation, what changes when you are trading someone else's money under a drawdown rule, and the sizing mistake that quietly ends more evaluations than bad entries do.

Size from the stop, not from the account

Most traders pick a contract count and then find a stop. That is backwards, because it means your risk changes with every trade depending on how far away the stop happens to be. A tight scalp and a wide swing entry at two contracts each are two completely different bets.

Do it the other way round. Decide what a losing trade costs you, in dollars, before you look at the chart. Then let the stop distance decide the size.

contracts = risk per trade in dollars, divided by (stop distance in ticks x tick value)

You need the tick value of what you trade. These are the CME specifications for the common futures contracts.

A worked one. You risk $200 a trade, you are trading MNQ, and your stop is 20 points away. Twenty points is 80 ticks at $0.50, so $40 of risk per contract. $200 divided by $40 is five contracts.

Move the stop to 40 points on the next trade and the same $200 buys you two contracts, with a bit left over. Your risk did not change. That is the whole point of doing it this way: every trade in your history becomes comparable, which is what makes an expectancy figure mean anything at all.

Always round down. Two and a half contracts is two. Rounding up is a decision to exceed your own risk limit, and it is the one place in this arithmetic where people reliably cheat.

On a prop account, the drawdown sets your risk

This is where the standard advice stops working.

"Risk one to two percent of your account" comes from investing, where the account is your money and losing 30 percent is survivable. A funded futures account is not that. You do not have $50,000 to lose. You have a buffer, and when the buffer is gone the account is gone, along with whatever you paid for it.

On a Topstep 50K Combine the maximum loss limit sits $2,000 below your starting balance. That is the number that matters. It is 4 percent of the headline account size, so one percent of $50,000 is $500 a trade, and $500 a trade means four losing trades ends you.

Four consecutive losers is not a disaster scenario. At a 40 percent win rate it is a 13 percent event on any given group of four trades. You will meet it in your first fortnight.

So size against the buffer instead, and ask how many losses you want to survive.

Ten consecutive losers at a 40 percent win rate is roughly a one in 400 sequence. Twenty is effectively never. That is the trade you are making: a smaller number takes longer to reach the profit target and makes the account very difficult to lose.

A reasonable default is risk no more than a tenth of your drawdown buffer on any trade. On a $2,000 buffer that is $200. It is not a magic number, it is just the point where an ordinary losing streak stops being fatal.

The daily limit is a second, separate cap

Most firms also run a daily loss limit, and it constrains you differently. The trailing drawdown asks how many losses you can take in total. The daily limit asks how many you can take today.

Topstep's 50K daily loss limit is $1,000. If you plan to take five trades in a session, five full losers at $200 is exactly $1,000 and you are done for the day at your fifth stop. That works. If you risk $400 and take five trades, you are finished after two and a half, which in practice means you get stopped out twice and then spend the session unable to trade the setup you were waiting for.

maximum risk per trade = daily loss limit divided by the number of trades you will actually take

Run both calculations and take the smaller answer. On the 50K numbers, the buffer says $200 and a five-trade day says $200, so they agree. On a firm with a tight daily limit relative to the drawdown, the daily number will bind first. There is more on how these interact in the daily loss limit explained and trailing drawdown explained.

This is what micros are for

With $200 of risk and a 20 point stop on the Nasdaq, one NQ contract risks $400. You cannot take the trade. Five MNQ risks $200, and you take it exactly as planned.

Micros are not a beginner's contract. They are the tool that makes correct sizing possible on a small account, and the ability to add a sixth contract rather than jumping from one to two is worth far more than it looks. It is the difference between a risk model and a rounding exercise.

The cost is real but small, and worth naming: micros carry a much higher fee per tick than the full-size contract, so if you take small targets the commission eats a meaningful slice of the trade. The numbers are in what futures commissions actually cost. Size correctly with micros anyway. Paying a fee is survivable, being unable to size is not.

Four ways this goes wrong in practice

Sizing up after wins

It feels like pressing an edge. What it does is guarantee your biggest bets land during the runs you cannot predict, which turns a positive expectancy into a coin flip on timing. If you want to scale with the account, scale from the buffer as it grows, on a schedule, not from how the last three trades felt.

Sizing up after losses

Worse, and much more common than anyone admits. It is the same trade twice, once with the risk doubled and once with your judgment impaired. If you find yourself computing what it would take to get back to flat, that is the signal to stop for the day, not to size up.

Moving the stop instead of cutting the size

A wide setup with a small position is a legitimate trade. A wide setup with a stop pulled in to justify a big position is a different trade with a much lower win rate, and it will not look like a sizing error afterwards. It will look like your strategy stopped working.

Forgetting the open position when you add

Adding to a winner is fine if the combined risk still fits your number. Two positions sized independently at your full risk is a double-size trade you did not decide to take. Size the total, not each entry.

Do this once, then use it every day

1. Find your real buffer. Not the account's headline size, the distance to the drawdown line right now.
2. Divide it by ten. That is your maximum risk per trade.
3. Divide your daily loss limit by the number of trades you take in a session. If that is smaller, use it instead.
4. Before each trade, take the stop distance in ticks, multiply by tick value, and divide your risk figure by it.
5. Round down. Take the trade or skip it.

Steps one to three change perhaps once a month. Step four takes a few seconds and is worth doing before the entry rather than after, because the number is much easier to respect when you worked it out before you had a position.

The check that tells you whether any of it is holding is in your own history: your average losing trade should be close to 1R. If your losers average 1.4R, the stops are not being honoured, and no sizing rule survives that. It is the first thing worth looking at in a month of trades, and it is the one most people never check.

The short version

• Contracts = risk in dollars, divided by stop in ticks times tick value. Round down.
• On a funded account, size against the drawdown buffer, not the headline account size.
• A tenth of the buffer per trade survives an ordinary losing streak. A quarter of it does not.
• Check the daily limit separately and take whichever cap is smaller.
• Never size up to fix a loss, and never pull the stop in to fit a size.

Our position size calculator runs this for the main prop firm account types, and the trailing drawdown calculator shows where your line actually sits today. Aurafy tracks your realised risk per trade from your imported fills, so you can see whether the sizing you planned is the sizing you traded, and the journal is free.