Position Size & Reward-to-Risk Calculator
Position sizing is the part of trading most beginners skip and most professionals obsess over. The two calculators below help you answer the questions that actually decide whether a strategy survives a losing streak: how many lots should I trade given a fixed rupee risk, and is this trade's reward worth its risk. Everything runs in your browser — nothing you type is sent anywhere.
Position Size
For a short (e.g. selling an option) the stop sits above the entry; for a long it sits below. The calculator uses the absolute distance either way.
Reward-to-Risk
The break-even win rate is the minimum percentage of trades you must win, at this reward-to-risk ratio, just to avoid losing money (before costs).
How to size a position
The method these calculators use is the standard fixed-fractional approach:
- Decide the rupee amount you are willing to lose on one trade — usually a small fixed percentage of capital (1–2% is common).
- Measure the distance from your entry to your stop-loss. That is your risk per unit.
- Divide the rupee risk by the per-unit risk to get the number of units, then round down to a whole number of lots so you never exceed your intended risk.
This keeps your loss roughly constant across trades regardless of how wide or tight the stop is, which is what lets a strategy survive an inevitable run of losers. For more on why this matters, see Risk Management in Algorithmic Trading and Choosing Between 1:2, 1:3 and 1:5 Targets.
Note on lot sizes: NSE revises F&O lot sizes periodically — always confirm the current lot size for your contract on the NSE derivatives page before trading. The default of 75 is shown only as an example.
This calculator is an educational tool, not investment advice. It does not account for brokerage, taxes, slippage or margin requirements. Trading in derivatives carries a high risk of loss. See our Risk Disclaimer.