Position Sizing: The Maths Every Trader Should Know

Ask most new traders what they are working on and they will tell you about entries. Ask a trader who has survived a few years and they will tell you about size. Position sizing — how much you put on a single trade — is what actually decides whether one bad trade is a scratch or a disaster. It is also simple maths. This is an educational article, not financial advice.

The one formula

Position sizing works backwards from risk, not forwards from conviction:

Position size = (account × risk %) ÷ risk per unit

• Account × risk % is the money you are willing to lose if the trade hits its stop. A common, conservative starting point is 0.5%–2% of your account per trade.
• Risk per unit is the loss on one share/lot/contract if price moves from your entry to your stop.

Divide the first by the second and you get how many units keep your loss inside the limit you chose. That is the whole idea: you decide the loss first, and size follows.

Worked examples

Stocks. ₹5,00,000 account, risking 1% (₹5,000). Entry ₹200, stop ₹190 → risk per share ₹10. Position = 5,000 ÷ 10 = 500 shares. If the stop hits, you lose ₹5,000 — the amount you chose, no more.

F&O / intraday. Treat one lot as your unit and the loss per lot at your stop as the risk per unit. Risking ₹5,000 with a stop that costs ₹2,500 per lot → 5,000 ÷ 2,500 = 2 lots. The maths is identical; only the unit changes.

Forex. Risk ÷ (stop in pips × pip value per lot). $10,000 account risking 1% ($100), 20-pip stop, $10 per pip per standard lot → 100 ÷ (20 × 10) = 0.5 standard lots. Our forex lot size calculator handles standard, mini and micro lots.

You can run any of these instantly with the free position size calculator — enter account, risk %, entry and stop and it returns the size and your risk/reward.

Why this matters more than your entry

A great entry with reckless size still blows up; a mediocre entry with disciplined size survives to trade again. When every trade risks the same small fraction, a losing streak is uncomfortable but not fatal, and your edge — if you have one — has time to show up. Fixed-lot sizing does the opposite: a wide stop quietly risks far more than a tight one, so your losses swing unpredictably.

Check your own sizing

Knowing the formula is one thing; applying it consistently is another. The honest test is your own history: were your actual losses roughly the same size, or all over the place? Our free Trader Health Check reads your exported trades and scores your position sizing (and loss discipline, overtrading and cost drag) so you can see whether you actually sized by risk or by feel. Educational only, not a broker, and it never asks for your broker password.

Takeaway

Position sizing is not advanced — it is arithmetic you do before you enter. Decide the loss, divide by the risk per unit, trade that size. It won't guarantee profit; nothing can, and trading carries a real risk of loss. But it is the difference between an account that can compound and one that a single trade can end.

Educational only — not financial advice. Nothing here is a recommendation to buy or sell, and no outcome or return is promised or implied.