Options position size calculator
How many lots to trade, worked out from your account size, the risk you are willing to take, and how far away your stop is — not from how confident you feel or how much margin your broker will allow.
Too big for this account
One lot risks about ₹4,388, which is more than 3% of ₹1,00,000. Sizing to a single lot anyway would put more at risk on one trade than the plan allows.
The 0.5 delta is an at-the-money approximation — it is stated here rather than hidden because the suggestion is only as good as that assumption. A deep out-of-the-money leg has a much lower delta and this will undersize it.
The rule it applies
Size follows from three things: the rupee amount you are prepared to lose, the distance to your stop, and the lot size of the contract. Conviction is not one of them, because conviction is not measurable and is highest precisely when it is least reliable.
The stop distance here is 1.5× ATR, so size adapts to conditions automatically: when volatility rises the stop widens, and the same rupee risk buys a smaller position.
The correction most calculators miss
Per-lot risk is capped at the premium
A generic calculator divides your risk budget by the stop distance in points. For an option buyer that overstates the risk, because a long option cannot lose more than the premium paid. Per-lot risk is therefore the lower of the stop-distance figure and premium × lot size. Without the cap you undersize every trade where the stop is wide relative to the premium — which is most of them on a cheap weekly option.
Why not just use available margin?
Margin tells you the largest position you can open, which is unrelated to the largest you should. The two diverge most dangerously when the stop is tight, because that is exactly when the margin figure permits the most lots.
The arithmetic that makes this matter: risking 2% per trade, eight consecutive losses costs about 15% of the account and is recoverable. At 10% per trade the same streak costs around 57%, and recovering from that requires roughly doubling what is left. Same strategy, same streak, different outcome — entirely because of size.
A sizing calculation is arithmetic over the inputs you supply, not a recommendation to take any trade. Educational and analytical content only. OptionLab Pro is not a SEBI-registered investment adviser or research analyst and does not give buy or sell recommendations. Derivatives trading carries a high risk of loss.