Position sizing: how much could you lose on one trade?

By the Blockhorizon Editorial Team · Updated 2 October 2026 · How we check facts

Most beginners start by asking “how much could I make?”. Position sizing starts from the opposite question: if this trade goes wrong, how much money am I prepared to lose? This lesson is pure arithmetic. All prices below are illustrative — made up to show the calculation — and nothing here is a trading strategy.

What is position sizing?

Your position is how much of a crypto-asset you hold in a trade. Position sizing is deciding that amount before you trade, based on two things you choose in advance:

• Risk amount — the money you are prepared to lose on this one trade.
• Exit price — the price at which you plan to sell if the trade goes against you, often set with a stop order.

The distance between your entry price and your exit price tells you how much you lose per coin. Divide your risk amount by that distance, and you get the number of coins to buy.

How do you calculate position size for a crypto trade?

Three formulas, in order:

1. Risk amount = account balance × risk percentage
2. Loss per coin = entry price − exit (stop) price
3. Position size (coins) = risk amount ÷ loss per coin

Then check it: position size × loss per coin should equal your risk amount. And position value = position size × entry price tells you how much money the trade ties up.

This works for a simple purchase (a “long” position) without borrowing. Leverage changes the picture — see below.

What does a worked example look like?

Illustrative example 1. Balance $5,000. You decide to risk 1% on one trade. Bitcoin (BTC) is at an illustrative $60,000 and you plan to exit at $57,000.

• Risk amount = 5,000 × 0.01 = $50
• Loss per BTC = 60,000 − 57,000 = $3,000
• Position size = 50 ÷ 3,000 = 0.016667 BTC
• Position value = 0.016667 × 60,000 ≈ $1,000
• Check: 0.016667 × 3,000 ≈ $50 ✔

Notice that the trade ties up about $1,000, but the planned loss is $50. Those are two different numbers, and mixing them up is a common beginner mistake.

What happens if you move your stop further away?

Illustrative example 2. Same $5,000 balance and $50 risk, but the exit is set at $54,000.

• Loss per BTC = 60,000 − 54,000 = $6,000
• Position size = 50 ÷ 6,000 = 0.008333 BTC (about $500 of BTC)

A wider stop means a smaller position for the same money at risk. A tighter stop means a bigger position — but a stop placed close to the current price can be triggered by short-lived price swings, as FINRA warns in our order types lesson.

Illustrative example 3. Same trade as example 1, but you choose 2%: risk amount = 5,000 × 0.02 = $100, so position size = 100 ÷ 3,000 = 0.033333 BTC (about $2,000).

Is the 1–2% rule an official rule?

No. You will often see “risk no more than 1–2% per trade” online. That is a convention some traders use, not a law and not a regulatory standard. None of the regulator material we reviewed for this lesson sets a maximum percentage of your account to risk on a single trade. The 1% and 2% figures on this page are only there to make the arithmetic concrete.

What regulators do say is more basic: the UK Financial Conduct Authority (FCA) says that if you invest in crypto, “you should be prepared to lose all your money”. The percentage you put at risk on each trade is a personal decision.

How do fees and the spread change the numbers?

The formula above ignores costs. Real trades usually have a trading fee and a bid-ask spread, and both add to your loss if the stop is hit.

Illustrative: take example 1 and add a 0.5% trading fee on each side.

• Fee to buy: $1,000 × 0.005 = $5.00
• Value at the stop: 0.016667 × 57,000 ≈ $950, so the fee to sell = 950 × 0.005 = $4.75
• Loss if the stop fills exactly: $50 + $5.00 + $4.75 = $59.75, not $50

If you want the total, including costs, to stay at $50, size the position slightly smaller. Our guide to crypto trading fees explains where these costs come from.

Why does a run of losses matter even with small risk per trade?

Because losses compound. Illustrative arithmetic, starting at $10,000 and risking a fixed percentage of the current balance each time:

And getting back is harder than falling. The gain needed to recover a loss = 1 ÷ (1 − loss) − 1:

• a 10% loss needs an 11.1% gain to recover;
• a 25% loss needs a 33.3% gain;
• a 50% loss needs a 100% gain.

What if the formula says to buy more than you have?

With a very tight stop, the formula can produce a position bigger than your balance. Illustrative: $50 risk with an exit only $600 below a $60,000 entry gives 50 ÷ 600 = 0.083333 BTC — about $5,000, your entire balance.

Going further would mean borrowing (leverage). The US Commodity Futures Trading Commission (CFTC) warns that when markets go against leveraged positions, customers “will be forced to refill their margin accounts or close out their positions, and in the end may lose more than their initial investments”. Leverage also makes small price moves matter much more, so the arithmetic on this page no longer tells the whole story.

What are the limits of position sizing?

• A stop is not a guaranteed exit price. A stop order turns into a market order when triggered, and the SEC’s Investor.gov says “The stop price is not the guaranteed execution price for a stop order.” Australia’s ASIC notes that stop-loss orders “can limit your losses, but you may also pay a premium price to guarantee your stop loss order.”
• Gaps can double the loss. Illustrative: in example 1, if the price falls through $57,000 and your order fills at $54,000, the loss is 0.016667 × 6,000 = $100 — twice the planned $50.
• Crypto is volatile. The FCA says crypto-assets “tend to be very volatile, so it’s hard to pinpoint their value from one day to the next.” See crypto volatility explained.
• It does not make a trade a good idea. Position sizing limits how much a single planned loss costs; it says nothing about whether the trade should be taken.

Blockhorizon is an education site. Nothing here is a recommendation to trade or a promise about results.