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Position size calculator

Decide what a wrong trade may cost before you open it. The calculator turns that into shares, forex lots or CFD contracts.

The share of your account you lose if the stop is hit

Buy

Money at risk
Risk per share
Position value
Share of account
Reward : risk

What could a losing streak at this risk do? Run the risk simulator

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How to use the calculator

  1. Pick the tab for what you trade: Shares / ETFs, Forex or CFD / index.
  2. Enter your Account size: the money in the account you trade with, not your total savings. For forex and CFDs, also pick the Account currency.
  3. Set Risk per trade: the share of the account you accept to lose if the trade fails. Around 0.5–2% is common among people who manage risk seriously.
  4. Enter the Entry price and where your reason for the trade is proven wrong: the Stop-loss price for shares, or a stop in Pips or Points (or as a Price) for forex and CFDs. For shares, put the stop below the entry for a long position and above it for a short one; in the other tabs choose Buy (long) or Sell (short).
  5. Forex: check the Pip size and the exchange rate (filled in when it can be worked out from the price). CFDs: enter the Value of 1 point per contract from your broker's contract details.
  6. Trade the size shown, not more. Read the warnings: a position bigger than your account, a margin that eats most of the account, or a target closer than your stop is a reason to rethink the trade.

What it's good for

  • Every loss is decided in advance and kept small, so no single trade can seriously damage your account.
  • Removes emotion from the most important decision: how much to buy.
  • One method for shares, forex lots and CFD contracts, so trades of any size compare on the same footing.
  • Rounds down to your broker's smallest trade size and shows the real risk after rounding.
  • Shows the margin at the EU retail limit, so you see when a tight stop makes a position oversized.

Where it falls short

  • A stop-loss isn't guaranteed: prices can jump past it overnight, at the weekend or on news, and the loss is then bigger than planned.
  • It ignores spreads, commissions, overnight financing and currency conversion, which make every trade a little more expensive.
  • There are no live prices: for cross-currency forex trades you type the exchange rate yourself.
  • Brokers' contract sizes and minimum steps differ; check yours before trading.
  • Correct sizing makes losses survivable. It doesn't make a bad trading idea good.

How it's calculated

Formula. Size = (account × risk %) ÷ (stop distance × money per unit of distance), rounded down to the smallest trade size. Shares: distance = |entry − stop| per share. Forex: pip value per unit = pip size × (1 quote currency in account currency); lots = units ÷ 100,000. CFDs: money per point = value per point × exchange rate. Margin = position value ÷ the EU leverage limit. Reward : risk = |target − entry| ÷ |entry − stop|.

Worked example. 10,000 account, 1% risk, entry 50, stop 47.50: you may lose 100, the risk per share is 2.50, so you buy 40 shares (2,000). With a target of 57.50 the reward:risk is 3:1. Forex: EUR/USD with a USD account and a 50-pip stop gives 0.20 lots (20,000 units), margin 733.33 at 30:1; USD/JPY at 150 with a 30-pip stop gives 0.50 lots.

Assumptions.

  • The stop is filled at its price; gaps can make losses bigger.
  • Spreads, commissions, financing and currency costs aren't included.
  • Exchange rates you type are used as they are; nothing is fetched live.

Formula checked 2026-10-23 and covered by automated tests. See the editorial policy and methodology.

The idea in one line

You don't choose how big the trade is. You choose how much you're willing to lose, and where you'll admit you're wrong. The size follows from those two, whether you count shares, lots or contracts.

The formula: size = (account × risk %) ÷ (stop distance × money per unit of distance). For shares, one unit of distance is one unit of price per share. For forex it's one pip per currency unit; for CFDs, one point per contract.

Worked example for each tab

  • Shares / ETFs. 10,000 in the account, 1% risk, entry 50, stop 47.50: you may lose 100 and each share risks 2.50, so you buy 40 shares.
  • Forex, EUR/USD with a USD account. 1% of 10,000 = 100. A pip is 0.0001, so one standard lot (100,000 units) moves 10 USD per pip. A 50-pip stop costs 500 per lot, so you trade 0.20 lots = 20,000 units. At 1.1000 that position is worth 22,000 USD; at the EU limit of 30:1 the margin is 733.33 USD.
  • Forex, USD/JPY at 150.00 with a USD account. A pip is 0.01 yen, and one yen is worth 1/150 USD, so a standard lot moves 100,000 × 0.01 ÷ 150 = 6.667 USD per pip. With 100 at risk and a 30-pip stop you trade 0.50 lots. (Done carelessly on a computer, this sum comes out as 0.4999999… and rounds down to 0.49 lots. The calculator cleans that up first, and an automated test checks it.)
  • CFD / index. 1% of 10,000 = 100, a 50-point stop and 1 per point per contract: 2 contracts. At 18,000 that's 36,000 of exposure, and the margin at 20:1 is 1,800.

Why this matters more than picking winners

Most beginners spend all their time on what to buy and none on how much. But a few oversized losses can undo months of good decisions. Losses also hurt more than they look: after a 50% loss you need a 100% gain just to get back to even. Fixed small risk per trade keeps you in the game long enough for the good ideas to work.

Leverage: the margin is not your risk

With forex and CFDs you only put up a margin, for example 1/30 of the position for a major currency pair at the EU retail limit. That makes it tempting to size by "how much margin do I have". Don't: the margin says how big a position you're allowed to open, not how much you can lose. Your stop and your risk % decide that. If the margin needed is a large part of your account, the position is too big for your stop, or the stop too tight for normal price swings.

In 2018 EU regulators found that 74–89% of retail CFD accounts typically lose money. That's why providers in the EU must show their own percentage on their website, and why leverage for retail clients is capped (30:1 for major pairs, 20:1 for other pairs, gold and major indices, 10:1 for other indices and commodities, 5:1 for shares and 2:1 for crypto). Before you trust any broker with money, check it's on the regulator's register: how to check a broker in 3 steps.

What I've learned about risk

  • Pick the stop first, from the chart or your reason for buying, not from how much you'd like to buy. A stop placed "so the position fits" is just a hope.
  • Small risk feels boring. That's the point. Around 0.5–2% per trade is common among people who manage risk seriously; above that, a normal losing streak gets painful fast.
  • Losing streaks are normal. Even a solid approach that wins 40% of the time will regularly see 6 or more losses in a row. The win rate calculator shows how often.
  • Gaps ignore your stop. If a price opens far beyond your stop after news or over a weekend, you lose more than planned. Size so even that wouldn't break you.

Questions

What's the difference between a lot and a unit?
A unit is one unit of the first currency in the pair: 20,000 units of EUR/USD means 20,000 euros' worth. A standard lot is 100,000 units, a mini lot 10,000 and a micro lot 1,000. Most brokers let you trade in steps of 0.01 lot, which is 1,000 units.
What is a pip?
The usual smallest price step quoted for a currency pair: 0.0001 for most pairs and 0.01 for pairs priced in Japanese yen. Many brokers show one extra digit (a "pipette"), so 1.10005 is half a pip above 1.1000.
Why does the stop set the size, not the other way round?
Because the stop is where the market proves your idea wrong, and that depends on the chart, not on your account. If you move the stop to make a bigger position fit, you've turned a planned loss into a hope. Keep the stop where it belongs and let the size shrink.
Why do I have to type the exchange rate?
The calculator doesn't fetch live prices, so nothing you type ever leaves your browser. When the pair is priced in your account currency the rate is simply 1, and when your account currency is the first one in the pair (USD/JPY with a USD account) it's 1 ÷ the price, so those are filled in for you. For other combinations, type today's rate from your broker.
Does it work for short positions?
Yes. In the Shares / ETFs tab, put the stop above the entry; in the Forex and CFD / index tabs, choose Sell (short). Shorting has its own risks, including losses that can exceed what you planned if the price jumps.
Why is the money at risk slightly lower than my %?
Shares come in whole numbers and brokers have a smallest trade size for lots and contracts, so the calculator rounds down. Rounding down means you never risk more than you chose.
Do fees count?
Not in this calculator. Spreads, commissions, overnight financing and currency conversion make each trade more expensive, especially for small amounts and positions held for days.

Sources · last checked

Formula: see "How it's calculated" above; tested against the worked example shown there.

Last reviewed

Education, not advice. I'm not a financial adviser and I don't know your situation. These tools show the maths behind common rules of thumb; check important decisions with a qualified professional. Full disclaimer.