How to Calculate Lot Size From Your Risk: Forex and Index CFDs on MT5

Ask ten part-time traders how they choose their lot size and you will hear ten answers. “I always trade 0.1.” “I trade 1 lot on indices and 0.5 on gold.” “It depends how confident I am.” Each of those answers means the amount at risk changes from trade to trade, usually in the wrong direction: bigger after a win, smaller after a loss, and biggest on the trade you feel most sure about.

There is a simpler way, and it is the one professional risk managers use. Decide what you are willing to lose on the trade first. Then let the stop distance decide the lot size. This article shows the formula, works through a forex and an index example, explains where to find the numbers in MetaTrader 5, and looks at what different risk levels mean over a losing run.

Risk First, Lot Size Second

Every trade with a stop has a fixed worst case: the distance from the entry to the stop, multiplied by what each unit of that distance is worth. You control that worst case with the lot size.

Most traders express risk as a percentage of the account balance, typically between 0.5% and 2% per trade. On a $10,000 account:

• 1% risk is $100
• 1.5% risk is $150
• 2% risk is $200

That amount is the same whether the stop is 20 pips away or 200. A wider stop simply means a smaller position.

The Formula

Lot size = money at risk ÷ (stop distance in ticks × tick value per lot)

Two numbers come from the instrument itself:

• Tick size is the smallest price step, for example 0.00001 on EURUSD with five decimals.
• Tick value is what one tick is worth for one lot, in your account currency.

The stop distance in ticks is the price distance from entry to stop, divided by the tick size.

Traders often work in pips instead of ticks. That is fine as long as you use the pip value that matches: on most five-decimal forex pairs, one pip is ten ticks.

Example 1: EURUSD

Account balance $10,000, risk 1%, so $100 at risk.

• Buy limit at 1.08500, stop at 1.08000: a distance of 0.00500, which is 50 pips.
• For a standard lot of EURUSD in a USD account, one pip is worth about $10.
• Lot size = $100 ÷ (50 pips × $10) = 0.20 lots.

If the stop were 25 pips, the same $100 would allow 0.40 lots. If it were 100 pips, 0.10 lots. The risk stays at $100 in every case.

For pairs where the quote currency is not your account currency, such as USDJPY or EURGBP in a USD account, the pip value changes with the exchange rate. That is exactly why it is better to read the tick value from the platform than to remember a fixed number.

Example 2: A US Stock Index CFD

Index CFDs are where fixed lot habits do the most damage, because contract sizes differ from broker to broker. On one broker, one lot of a US 500 index CFD might be worth $1 per index point. On another, it might be $10 per point, or $50.

Take an example where one lot is worth $1 per point, with a tick size of 0.1 and a tick value of $0.10.

• Account balance $10,000, risk 1%, so $100 at risk.
• Buy limit at 6,500.0, stop at 6,320.0: a distance of 180 points, which is 1,800 ticks.
• Lot size = $100 ÷ (1,800 ticks × $0.10) = 0.55 lots.

On a broker where one lot is worth $10 per point, the same trade would be 0.05 lots. Trade “1 lot” on both and the risk is ten times different. This is why the contract specification matters more than any rule of thumb.

Where to Find the Numbers in MetaTrader 5

In MT5, open the Market Watch window, right-click the symbol and choose Specification. The window shows, among other things:

• Contract size: how many units one lot represents
• Tick size and tick value
• Minimum volume: the smallest lot size you can trade
• Volume step: the increments in which you can size a position, for example 0.01

Check these once for every instrument you trade, and again if your broker announces a contract change. Two brokers can use the same symbol name for contracts of different sizes.

Always Round Down

The formula almost never produces a lot size that matches the volume step exactly. If it gives 0.237 lots and the step is 0.01, you trade 0.23, not 0.24. Rounding up means risking more than you decided to.

Sometimes rounding down changes the risk a lot. If the formula gives 0.014 lots and the minimum is 0.01, you risk about 30% less than planned, which is acceptable. If it gives 0.007 lots and the minimum is 0.01, the smallest possible trade risks over 40% more than you planned. In that case the honest answer is not to take the trade at all. A sensible rule: skip a trade when rounding changes the risk by more than about 20%.

What Changes the Real Risk

The formula gives the planned risk. A few things can make the real loss larger:

• Spread. Your stop is triggered on the bid for a long and the ask for a short. In wide-spread moments, around the rollover or news, a stop can fill earlier than the chart suggests.
• Gaps. Over a weekend or after major news, price can jump past the stop. The order fills at the next available price.
• Slippage on a fast market.

None of these are reasons to skip a stop. They are reasons not to sit at the very top of your risk range.

How 1%, 1.5% and 2% Feel Over a Losing Run

Every strategy has losing runs, including good ones. Here is what a run of consecutive full losses does to a $10,000 account at each level, with each loss taken from the shrinking balance:

Losses in a row	1% risk	1.5% risk	2% risk
5	-4.9%	-7.3%	-9.6%
10	-9.6%	-14.0%	-18.3%
15	-14.0%	-20.3%	-26.1%

Ten losses in a row sounds unlikely until it happens. For a strategy that wins six trades in ten, a run of five or six losses will show up from time to time over a few hundred trades, and longer runs are possible.

The numbers in the table are not only about money. At 2% risk, a bad run takes away almost a fifth of the account, and that is when traders start to skip setups, double up to win it back, or abandon a method that was working. Many traders start at 1%, and only raise their risk after their own results have tracked the method’s tested results for a while.

A Checklist for Every Trade

1. Decide the risk percentage before you look at the chart.
2. Place the stop where the strategy says, not where it gives the lot size you want.
3. Calculate the lot size from the instrument’s tick value and tick size.
4. Round down to the volume step.
5. Skip the trade if the minimum volume pushes the risk far above your plan.

Where PriceEdge Fits

Every PriceEdge setup comes with lot sizes for 1%, 1.5% and 2% risk, calculated from your broker’s own contract data and your balance, and rounded down. When the minimum volume would change the risk too much, the setup says the size is not viable instead of quietly sizing up. The Scorecard then compares your own months with the backtest, so you can see when your results justify moving from 1% to a higher risk level.

You can try it for 60 days on a demo account, with no credit card.