Theta
Option theta is the modelled change in option value as time passes, holding other inputs constant.
Plain-language meaning
Option theta is the modelled change in option value as time passes, holding other inputs constant.
Why it is useful
Theta is useful as descriptive evidence when it is compared on the same definition, source, period, unit and exact listing. It is one input to research, not a verdict.
Where it appears in XMarketRadar
Look for Theta in Futures, Option Chain, Options Screener and derivative study tables for a selected underlying and contract.
How it is calculated or sourced
XMarketRadar calculates Theta locally with Black-Scholes-Merton using spot, strike, years to expiry, NSE-published implied volatility and a fixed 7% risk-free-rate assumption. NSE supplies IV, not the Greek. The implementation has no dividend-yield input; theta is per day and vega per one volatility-percentage-point change.
Inputs, period and unit
Read the disclosed inputs or source, observation period, bar interval, unit, native currency and scale. A value without its source and as-of context is incomplete; unlike units must not be combined.
Worked example
Illustrative only: Theta of −₹0.30 per day means the model attributes about ₹0.30 of value loss to one day passing, all else equal; real prices need not follow it.
What high and low mean
A higher or lower Theta value is descriptive, not automatically good or bad. Meaning depends on the instrument, comparison period, method and related evidence.
Positive, negative and genuine zero
Positive and negative Theta values retain the definition shown here. A genuine reported or computed zero is displayed as 0 and is not the same as missing evidence.
Limitations and common mistakes
Greeks and IV are model estimates, not guaranteed realized changes. XMarketRadar's Black-Scholes-Merton calculation assumes a fixed 7% risk-free rate and has no dividend-yield input; exercise style, carry, stale quotes or a different rate can materially change the result.
Market-specific differences
Contract size, exercise style, expiry, settlement, price unit and trading rules vary across all supported markets. Always use the selected contract specification.
Suggested next steps
Open the related Derivatives terms below, then follow the matching Help Centre task guide and inspect Theta on an exact exchange listing. Confirm source, as-of time, units and unavailable reason before using it in research.
Educational information only; not investment advice or an order service.
This Theta tutorial is educational and descriptive. It is not investment advice, a price prediction, a recommendation, or an instruction to buy, sell, rebalance or place an order.