Position Size Calculator
Know exactly how many shares or lots to trade before you risk a single rupee — with F&O-aware lot rounding, reward-to-risk scoring, Kelly Criterion sizing, portfolio heat tracking, and a losing-streak simulator built in.
| Symbol | Entry | Stop | Qty | Risk (₹) | Value (₹) |
|---|
Losses and the gains needed to recover from them are not symmetric — a 20% drawdown needs a 25% gain to recover, a 50% drawdown needs a 100% gain. This compounding asymmetry is the entire reason position sizing matters.
| Index | Current lot size |
|---|
How professional position sizing actually works
Risk amount ÷ risk per share
Position size = (Account × Risk%) ÷ |Entry − Stop|. The stop-loss distance, not your conviction about the stock, determines how many shares you can afford to buy.
Why professionals rarely exceed 2%
At 2% risk, a 10-trade losing streak costs ~18% of capital. At 10% risk, the same streak wipes out ~65%. Small percentages compound very differently on the way down.
Per-trade risk isn't total risk
Five "safe" 2%-risk positions opened at once is 10% of your account at risk simultaneously if they're correlated. Track heat across your whole book, not trade by trade.
- 01What is position sizing?
- 02Why position sizing matters more than stock-picking
- 03The position sizing formula, explained
- 04A worked example, step by step
- 05The 1-2% rule, and why it exists
- 06Portfolio heat: per-trade risk isn't total risk
- 07The Kelly Criterion: sizing from your own track record
- 08Common position sizing mistakes to avoid
What is position sizing?
Position sizing is the decision of how many shares or lots to buy or sell on any single trade. It is, deliberately, a separate decision from picking the stock or the direction — you can have an excellent entry signal and still damage an account by sizing the trade too large relative to capital. Most professional traders and risk managers consider position sizing the single most important decision in trading, more important than entry timing or even the win rate of the strategy itself.
This calculator uses the fixed-fractional risk model: you decide what percentage of your account you're willing to risk on a single trade, and the position size is derived from that percentage and the distance to your stop-loss — not from how confident you feel or how much capital happens to be sitting idle.
Why position sizing matters more than stock-picking
Consider two traders with identical stock-picking skill, both averaging the same win rate on the same setups. Trader A risks 2% of capital per trade. Trader B risks 15%. Over a long enough sequence of trades, including the inevitable losing streaks every strategy experiences, Trader A's account survives comfortably while Trader B's account can be functionally destroyed by a streak of losses that, statistically, was always going to happen eventually.
Position sizing doesn't make you right more often. It determines how much being wrong, when it inevitably happens, costs you — and whether your account survives long enough for your edge, if you have one, to play out over many trades.
The position sizing formula, explained
Position Size = (Account × Risk%) ÷ |Entry − Stop|
- Account — your total trading capital available for this position.
- Risk% — the percentage of that capital you're willing to lose if the stop-loss is hit. Most professional traders use 1–2% per trade.
- |Entry − Stop| — the absolute price distance between your planned entry and your stop-loss. This, not your conviction, is what ultimately determines position size.
For F&O positions, this calculator additionally rounds the resulting quantity down to the nearest whole lot, since you can't trade a fractional lot, and flags it clearly when the calculated size is smaller than one full lot.
A worked example, step by step
You have ₹1,00,000 in trading capital, you're willing to risk 2% per trade, your entry is ₹100, and your stop-loss is ₹90.
| Step | Value |
|---|---|
| Risk amount (1,00,000 × 2%) | ₹2,000 |
| Risk per share (100 − 90) | ₹10 |
| Position size (2,000 ÷ 10) | 200 shares |
| Total investment (200 × 100) | ₹20,000 |
Notice that the position uses only ₹20,000 of the ₹1,00,000 account — 20% of capital deployed, while only 2% is actually at risk if the stop is hit. This distinction, between capital deployed and capital at risk, is the entire point of risk-based sizing.
The 1-2% rule, and why it exists
Professional risk management rarely allows more than 1–2% of capital at risk on a single trade, for a reason that becomes obvious once you model out a losing streak — which every strategy, however good, will eventually have:
| Risk per trade | Drawdown after 10 straight losses |
|---|---|
| 1% | ~9.6% |
| 2% | ~18.3% |
| 5% | ~40.1% |
| 10% | ~65.1% |
A 65% drawdown requires a 186% gain just to get back to break-even — losses and the recovery needed from them are never symmetric. The losing-streak simulator built into this calculator lets you see this exact compounding effect for your own risk percentage.
Portfolio heat: per-trade risk isn't total risk
Sizing each trade individually at 2% risk feels safe, until you realise you might have five such positions open simultaneously — 10% of your account at risk at once, more if those positions are correlated (several stocks in the same sector tend to move together). Portfolio heat is the term for your total risk across every open position combined, and it's a number most retail traders never actually calculate, even though it's frequently the real reason an otherwise reasonable risk plan still produces an outsized account loss.
The Kelly Criterion: sizing from your own track record
If you have a genuine, sufficiently large trade history (30 or more real trades), the Kelly Criterion offers a mathematically derived "optimal" risk percentage based on your actual win rate and average win/loss ratio, rather than an arbitrary 1–2% rule of thumb. Full Kelly is widely considered too aggressive for real-world variance — most professional users apply half or quarter Kelly instead, which this calculator computes automatically alongside the full figure.
Kelly Criterion is only meaningful when your win-rate and ratio inputs come from real, sufficiently large trade history. Feeding it a guessed or hoped-for win rate produces a confident-looking but meaningless number.
Common position sizing mistakes to avoid
- Sizing based on how much you can afford to buy, not how much you're risking. "I have ₹50,000, so I'll buy ₹50,000 worth" ignores the stop-loss distance entirely and is not risk-based sizing.
- Widening the stop to fit a desired position size. Deciding you want 500 shares and then setting a stop wide enough to "afford" that size reverses the correct order of operations — the stop should come from the chart, the size from the stop.
- Ignoring portfolio heat across multiple open positions. Five trades at 2% each is 10% total risk, not 2%, especially if the positions are correlated.
- Increasing risk percentage after a losing streak to "win it back." This is precisely backward — risk should stay constant or decrease after losses, not increase.
How to use this calculator
- Enter your funds available and chosen risk percentage (1–2% for most professional approaches).
- Enter your entry price and stop-loss price — the distance between them drives the calculation.
- Switch to F&O mode for lot-based sizing on index derivatives, with automatic rounding to the nearest whole lot.
- Check the Kelly Criterion tab if you have real, tracked win-rate statistics.
- Use the Portfolio Heat tab to track total risk across every position you currently hold, not just the one you're about to add.
Frequently asked questions
A fixed percentage automatically scales with your account size, so the risk taken stays proportionate as your capital grows or shrinks. A fixed rupee amount would represent a shrinking percentage of a growing account (too conservative over time) or a growing percentage of a shrinking account (dangerously aggressive after losses) - neither of which is what a consistent risk plan should do.
Most professional traders and risk managers use 1-2% per trade as a starting point. Newer traders, or those trading more volatile instruments like F&O, often use the lower end of that range or less. There's no universally correct number, but exceeding 2-3% on a regular basis sharply increases the drawdown from any losing streak, as the table in the article above shows.
No. The position size shown is based purely on your risk amount and the entry-to-stop price distance. Brokerage, STT, exchange charges and slippage all add a small additional cost on top, which in practice makes your real risk very slightly higher than the theoretical figure shown here. Use the Accelpix Brokerage Calculator alongside this tool for exact, cost-inclusive figures.
The fixed-fractional model (the default calculation) uses a risk percentage you choose yourself, typically a conservative rule of thumb like 1-2%. The Kelly Criterion, found in its own tab, instead derives a suggested risk percentage mathematically from your own tracked win rate and win/loss ratio - but only produces a meaningful result if those inputs come from genuine, sufficiently large trade history.
The calculator will flag this clearly. It means your chosen risk amount, given the stop-loss distance, doesn't justify even one full lot at current prices - your real options at that point are to accept a larger risk percentage for this specific trade, find a tighter stop-loss level, or skip the trade entirely rather than force a lot size your risk plan doesn't support.
No. Portfolio heat approaching or exceeding 10% of account equity (the sum of risk across all simultaneously open positions) is generally considered the upper boundary by most professional risk frameworks, and many practitioners keep it considerably lower, particularly when positions are correlated.