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Second-order Greek—

Charm —

How Delta changes with the passage of time (Delta decay).

Quick answer: Charm measures how much an option's Delta changes as one day passes — the 'Delta decay' that quietly re-shapes your directional exposure over time, especially near expiry.

Simple explanation

Just as Theta decays an option's value with time, Charm decays its Delta. An option that is 0.40 Delta today might be 0.30 or 0.50 tomorrow purely because a day has passed, even if Nifty hasn't moved. Charm matters most for near-expiry options and for anyone holding a Delta-hedged position over time — including over weekends.

Charm — visual

How Charm behaves

Charm is near zero at-the-money and largest just in- or out-of-the-money near expiry, pushing Deltas toward 1 or 0 as time runs out.

ATM2320023850245002515025800Charm (Δ decay / day)Nifty spot
Measures
How Delta changes with the passage of time (Delta decay)
Sign
Signed by moneyness and time; near zero at-the-money
Typical range
Small far from expiry; grows sharply in the final sessions
Order
Second-order

Detailed explanation

Delta decay explained

Charm is the rate of change of Delta with respect to time. As expiry approaches, in-the-money options see their Delta drift toward 1 (calls) or −1 (puts), while out-of-the-money options see Delta drift toward 0. The option is 'making up its mind' about whether it will finish ITM, and Charm describes how fast that decision happens each day.

Why Charm spikes near expiry

Far from expiry, a day's passing barely changes Delta. But in the final sessions of a Nifty weekly, Charm becomes significant: a slightly-ITM call can gain Delta rapidly as expiry nears and its ITM finish becomes more certain, while a slightly-OTM call bleeds Delta toward zero. This is the directional cousin of Theta's value decay.

The weekend Delta drift

Charm acts over calendar time, so it operates across weekends and NSE holidays. A Delta-hedged trader who is flat on Friday can return on Monday to find the hedge is off because Charm shifted every strike's Delta over the closed days. Desks that run tight Delta hedges explicitly account for weekend Charm when setting Friday-afternoon hedges.

Practical use for position traders

Even without computing Charm, position traders feel it: a spread that seemed balanced drifts directional into expiry as the ITM and OTM legs' Deltas move apart. Recognising Charm explains why expiry-week positions need more frequent Delta checks and why 'set and forget' hedges fail as the clock runs down.

Formula

Charm formula

Charm = ∂Δ/∂t = −n(d₁) · (2rT − d₂σ√T) / (2Tσ√T)

Also called Delta decay or Delta bleed. Usually quoted per calendar day. Largest for near-expiry options slightly in- or out-of-the-money.

Practical example (Nifty)

Illustrative — Nifty spot 24500, lot size 75

It is Wednesday before a Thursday Nifty weekly expiry. You hold a 24,550 CE with Nifty at 24,500 — slightly OTM, Delta 0.45. Overnight nothing happens to Nifty, but Charm pulls the Delta down to about 0.38 by Thursday morning simply because there is now less time for it to finish ITM. If you were Delta-hedged with futures, you are now slightly net short and must adjust. Multiply this across a multi-leg book and the expiry-day hedging workload becomes clear.

Practical trading impact

  • Charm re-shapes your directional exposure over time even when price is still — plan for it near expiry.
  • It pushes ITM Deltas toward ±1 and OTM Deltas toward 0 as expiry approaches.
  • Delta-hedged positions drift out of balance across days, weekends and holidays because of Charm.
  • Expiry-week trades need more frequent Delta checks; 'set and forget' hedges decay directionally.

Common mistakes

  • Setting a Delta hedge before a weekend and assuming it holds — Charm shifts every Delta over the closed days.
  • Believing a balanced expiry-week spread stays neutral, when Charm pulls its ITM and OTM legs' Deltas apart.
  • Confusing Charm (Delta vs time) with Theta (value vs time) — both decay with time but measure different things.
  • Ignoring Charm on near-expiry books where it is large, while over-worrying about it far from expiry where it is tiny.

Professional usage

Expiry specialists on Indian desks watch Charm closely in the final two sessions: they pre-empt the Delta drift on ITM and OTM legs, adjust hedges on Friday for weekend Charm, and expect to re-hedge more often as expiry approaches. For discretionary traders, the professional takeaway is simple — check your Deltas daily in expiry week, because time alone is moving them.

Key takeaway

Charm is Delta decay — the way time alone re-shapes your directional exposure. It is negligible far from expiry and powerful in the final sessions, quietly turning balanced positions directional and knocking Delta hedges out of alignment across every closed session.

Frequently asked questions

What is Charm in options trading?
Charm measures how much an option's Delta changes as time passes, usually per day. It is also called Delta decay — the directional cousin of Theta's value decay.
Why does Charm matter near expiry?
Because Delta decay accelerates in the final sessions: ITM options' Delta drifts toward ±1 and OTM options' toward 0, changing your directional exposure quickly even without a price move.
What is the difference between Charm and Theta?
Theta is the decay of an option's value over time; Charm is the decay of its Delta over time. Both are driven by time passing but measure different sensitivities.
Does Charm act over weekends?
Yes. Charm works over calendar time, so Deltas shift across weekends and NSE holidays — a Friday hedge can be off by Monday.
Is Charm important for retail traders?
Mostly in expiry week. Near expiry, Charm noticeably re-shapes Deltas; far from expiry it is small enough to ignore for simple positions.
What is the difference between Charm and Vanna?
Both change Delta. Charm is Delta's sensitivity to time; Vanna is Delta's sensitivity to volatility.
How does Charm affect a Delta-hedged position?
It knocks the hedge out of balance over time. As Charm shifts each strike's Delta, a once-neutral book becomes directional and needs re-hedging.
Where is Charm largest?
For near-expiry options slightly in- or out-of-the-money. It is near zero at-the-money and small far from expiry.
Is Charm a first- or second-order Greek?
Second-order. It is the cross-derivative of the option price with respect to both the underlying and time.
How can I manage Charm risk?
Check Deltas daily in expiry week, re-hedge more frequently as expiry nears, and account for weekend Delta drift when setting Friday hedges.

Sources & references

Last reviewed 7 July 2026. Educational content only — not investment advice.

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Educational content only — not investment advice. Greek values are illustrative and computed from a Black-Scholes model. Options trading involves substantial risk. See our Risk Disclosure and SEBI Disclaimer.