Implied volatility is higher on the strikes far below the future, so the smile leans on the 30 Jun 2026 expiry
Start from a dated chain. Take a strike that traded, its settle price, the future for the expiry, the strike itself, the days to expiry and the rate on that date. Those five inputs are all the solver needs. The output is an annual volatility, quoted as a percentage.
The model is Black 76, Black's version from 1976 for options on a forward. It prices a call as the discounted expected payoff under a lognormal future. Volatility is the one input you cannot read off the market, so the solver searches. It starts from a guess, computes the model price, compares it with the settle price, and moves the guess until the two agree. A Newton step does most of the work, and a bisection fallback takes over when the Newton step runs away.
Three checks keep the answer honest. The price must be above intrinsic value, or no volatility will reproduce it. The strike must have traded, because an untraded strike's settle comes from the exchange's own model, so inverting it returns that model's volatility, not one the market paid. And the expiry time must be right: counting to the close, not the open, moves the answer for the short dated expiries.
The chart shows the implied volatility of each traded strike on the 10 Jun 2026 chain for the 30 Jun 2026 expiry. It is a smile. The strikes far below the future carry higher implied volatility than those near it, so the curve leans rather than sitting flat. The far upside rises a little too, which makes it a smile with a tilt.
The IV solver tool runs this search. Put in a settle price and it returns the volatility, so you can check a hand calculation against it.
Before you trade. Derivatives trading carries a high risk of loss. SEBI's study "Profitability of Individual Traders in the Equity Derivatives Segment (FY25 to FY26)" (August 2026) found that 87.7% of individual traders in equity F&O made net losses in FY26, with aggregate net losses of Rs 91,685 crore. Read the SEBI study