Stop Loss and Position Sizing for Intraday Trading
Part of Intraday Trading for Beginners (India): The Complete Guide
Every intraday trader has heard the advice to 'always use a stop-loss.' Almost none of them get taught what that actually means in practice, or how to decide how many shares to buy in the first place. Those two things, stop-loss and position sizing, are really one decision. Get them right together and a single bad trade costs you a small, known amount. Get them wrong and a single bad trade can wipe out a week of gains, or worse.
What a stop-loss actually is
A stop-loss is an order that sits on the exchange with a trigger price. When the market price touches your trigger, your order activates and tries to close your position. The word 'tries' matters here, because there are two kinds of stop-loss orders, and mixing them up is where most of the damage happens.
An SL order (stop-loss limit) has two prices: a trigger price and a limit price. When the trigger is hit, it places a limit order at your limit price. This means you control the worst price you will accept. The problem is that in a fast-falling or fast-rising market, the price can blow through your limit before your order gets filled, and you are left holding the position with no exit. You get price certainty, not exit certainty.
An SL-M order (stop-loss market) has only a trigger price. When the trigger is hit, it fires a market order, which fills at whatever price is available right then. You get exit certainty, not price certainty. For most intraday setups, especially in stocks that can move fast on news or low liquidity, SL-M is the safer default, because getting out matters more than getting out at an exact number. Reserve SL orders for liquid, large-cap names where slippage is usually small.
Trailing stop-loss is a variation on this. Instead of a fixed stop-loss price, it moves automatically as the trade moves in your favor. If you buy at ₹500 with a trailing stop-loss of ₹5, and the stock moves up to ₹520, your stop-loss trails up to ₹515. If the stock then reverses, you exit at ₹515 instead of giving back the entire move. A trailing stop-loss never moves against you, it only tightens in the direction of profit. This is how you let a winning trade run without needing to babysit the chart and guess when to book profit manually.
Why no stop-loss is the fastest way to blow up an account
Ask any intraday trader who has lost a large amount in a single day how it happened, and the answer is almost always the same: they were in a losing trade without a stop-loss, told themselves it would come back, and kept averaging down or just watching as the loss grew. Without a stop-loss, a trade has no defined worst case. One position can turn a normal trading day into a catastrophic one, and intraday leverage makes this worse, not better, because the same price move produces a bigger rupee loss on a leveraged position than on a plain cash position.
A stop-loss placed the moment you enter a trade, not after you start watching it lose money, removes this risk. It converts an unlimited, unknown loss into a fixed, known loss decided in advance, before emotion is involved.
Position sizing: the formula
Position sizing answers a different question: how many shares should you buy so that if your stop-loss is hit, the loss is one you can live with? The formula is simple.
- Risk per trade = (entry price - stop-loss price) x quantity
- Rearranged for quantity: Quantity = Risk per trade / (entry price - stop-loss price)
The 'risk per trade' in that formula should not be a random number. Most disciplined intraday traders fix it as a small percentage of total capital, commonly 1% to 2%, and never risk more than that on a single trade regardless of how confident they feel about it. This is what keeps a string of losing trades from turning into an account-ending event.
A full worked example
Say your total trading capital is ₹1,00,000, and you have decided to risk 1% of it per trade. That is ₹1,000 as your maximum acceptable loss if the stop-loss is hit.
- Total capital: ₹1,00,000
- Risk per trade at 1%: ₹1,000
- Entry price: ₹500
- Stop-loss price: ₹490
- Risk per share: ₹500 - ₹490 = ₹10
- Maximum quantity: ₹1,000 / ₹10 = 100 shares
So you buy 100 shares at ₹500. If the trade goes against you and the stop-loss at ₹490 is hit, you lose ₹1,000, exactly 1% of your capital, no more. If the stop-loss had been wider, say ₹480 instead of ₹490, your risk per share would be ₹20, and your maximum quantity would drop to 50 shares, because the formula always solves for the same ₹1,000 cap. A wider stop-loss means a smaller position. A tighter stop-loss means a larger position is allowed. The rupee risk stays fixed either way.
Where MIS margin and leverage fit in
Intraday orders on Tenth Trader, like in real MIS trading, use margin, meaning you can control a larger quantity than your capital would allow for a cash delivery trade. This is where many traders get the logic backwards. Leverage changes how much margin is blocked to hold a position, it does not change how much you should risk. The position sizing formula above already gives you the correct quantity based on your risk tolerance. Once you have that quantity, check whether the margin required to buy that many shares fits within your available capital. If leverage lets you afford more shares than the risk formula allows, the answer is not to buy more, it is to stick to the quantity the formula gave you. Using leverage to size up beyond your risk-per-trade limit is exactly how a ₹10 stop-loss on paper turns into a much bigger real loss, because you multiplied the quantity without changing the percentage risk logic that was supposed to protect you.
Bracket orders: automating the discipline
The math above is easy to follow when you are calm and looking at a spreadsheet. It is much harder to follow in the middle of a live trade, watching the price tick against you, telling yourself it will turn around. This is exactly the moment stop-loss discipline breaks down for most traders, and it is also exactly the problem a bracket order is built to solve.
A bracket order lets you place your entry, target, and stop-loss as one single order, all at the same time, before the trade even starts. Once your entry fills, the target and stop-loss are both already active on the exchange. You do not need to watch the position and decide when to exit, because the exit was already decided when you were calm and thinking clearly, not in the middle of a fast move when panic or hope take over. This is the practical answer to the fact that willpower is an unreliable risk management tool. A bracket order does not need willpower.
Drill this before real money is involved
Stop-loss placement and position sizing are simple arithmetic, but doing the arithmetic correctly, every single trade, under real time pressure, is a skill that takes repetition to build. A paper trading account that models real intraday costs, real margin rules, and real order types like SL, SL-M, trailing stop-loss, and bracket orders is the right place to run that repetition. Tenth Trader gives you ₹1,00,000 in virtual capital with live NSE prices and no signup, so you can place the same SL and SL-M orders, size positions with the same formula, and get the same margin behaviour you would face with real capital, without a single rupee of real money at risk. By the time you do trade with real capital, the position sizing formula should not be something you calculate, it should be something you do automatically, the same way you check a mirror before changing lanes.