Expiry & time6 min read

What Happens to Your Option Greeks Overnight

Between the 3:30 close and the next 9:15 open, time decay, Delta drift and volatility repricing keep working on your position even though you cannot trade.

By Bulan Sarkar · 25 April 2026

In short: Overnight, three things move your option position while the market is closed: Theta keeps decaying value across the calendar hours, Charm keeps shifting each strike's Delta so a balanced book drifts directional, and implied volatility can be re-priced at the open — often gapping up on overnight news or down as event uncertainty resolves. On top of that the index itself can gap, and Gamma means that gap hits your Delta harder near expiry. You are carrying real risk during the sixteen-odd hours you cannot do anything about it.

The market closes, but the clock does not

Black-Scholes prices options off calendar time to expiry, not trading hours, so time value keeps melting overnight and over weekends. If your long weekly option has a Theta of, say, minus 20, roughly that much value per share is gone by the next open even though nothing traded — a bit over ₹1,400 per lot at a 75-lot size. Sellers collect that decay; buyers pay it. This is why holding low-Delta long premium overnight, and especially over a Friday-to-Monday or a holiday gap, is expensive: you fund two or three days of decay for the chance of a move you cannot capture until the bell.

Charm quietly re-hedges your book against you

Charm is Delta decay — the way each strike's Delta drifts purely because time passed. Overnight, in-the-money options creep toward Delta 1 (calls) or minus 1 (puts) and out-of-the-money options bleed toward 0, so a spread that closed balanced can open leaning directional. A Delta-neutral trader who was flat at 3:30 may open net long or net short at 9:15 without the index having moved at all. Charm is small far from expiry and large in expiry week, so the overnight Delta drift on a Wednesday-before-expiry position is far bigger than on a fresh monthly.

The overnight gap: Delta meets Gamma

The most obvious overnight risk is a gap — the index opening well away from the previous close on global cues, overnight US moves, currency shifts or domestic news. Your loss or gain on the gap is roughly your position Delta times the gap, but Gamma makes that non-linear: a short ATM option that was minus 0.5 Delta at the close can effectively be far more exposed after a large gap, because Gamma steepened the Delta as price ran. This is precisely why short-Gamma sellers fear gaps — the move happens all at once, with no chance to hedge on the way, and the loss lands accelerated.

Volatility gets re-priced at the open

Implied volatility is not frozen overnight; it is reset when quoting resumes. If serious news breaks after hours, options can open with materially higher IV — a Vega windfall for long holders and a hit for sellers — even before the index moves much. Conversely, when a known event that had inflated IV passes overnight (a global central-bank decision, an election result, a big earnings print), IV can gap down at the open: the classic IV crush. A trader who bought expensive premium hoping for a move can open to find the volatility they paid for has evaporated, so the position loses despite being 'right'.

Events, weekends and holidays stack the risk

Overnight risk is not uniform — it clusters around the calendar. Holding through a night that contains a scheduled catalyst (RBI policy the next morning, US data, results from an index-heavy stock) stacks gap risk and IV-crush risk on top of ordinary Theta and Charm. Weekends and NSE holidays multiply the Theta and Charm because more calendar time passes with the market shut, and they extend the window during which news can accumulate unhedged. A three-day weekend before an event is the maximum-overnight-risk scenario for a premium buyer and, in a different way, for an over-sized premium seller.

What professionals do before the close

Desk traders decide their overnight posture deliberately rather than by default. They flatten or reduce Delta before the close if they do not want gap exposure, trim short-Gamma size ahead of nights with event risk, and set Friday hedges with the weekend's Charm and extra Theta already in mind. Long-premium holders weigh whether the expected overnight move justifies the guaranteed decay, and volatility traders check whether they are long or short Vega into a night that could reprice IV. The common thread is that carrying a position overnight is a decision with its own risk budget, not a neutral continuation of the day trade.

A practical overnight checklist

Before you leave a position on, ask four things. What is my net Delta, and how much do I lose on a plausible gap given Gamma? How much Theta and Charm will accrue by the open — and is it a weekend or holiday? Am I long or short Vega into any scheduled event that could crush or spike IV overnight? And is my size small enough to survive the worst realistic overnight move without forced action at the open? If you cannot answer these calmly, the position is too big or too exposed to hold across the close.

Key takeaways

Options price off calendar time, so Theta keeps decaying value overnight and over weekends — funding two or three days of decay for a move you cannot trade until the open.
Charm shifts every strike's Delta while the market is shut, so a balanced book can open leaning directional; the effect is large in expiry week.
Gap risk is Delta times the gap, made non-linear by Gamma — short-Gamma sellers fear gaps because the move lands all at once, accelerated, with no chance to hedge.
Implied volatility is re-priced at the open: news can gap IV up (a hit to sellers) or a passed event can crush it down, so long premium can lose despite being directionally right.
Risk clusters on the calendar — nights with scheduled events, and weekends or holidays, stack gap, IV and decay risk together.
Treat holding overnight as a deliberate decision: know your Delta, Gamma gap loss, accruing Theta and Charm, and Vega into any event before the close.

Frequently asked questions

Do options lose value overnight even if nothing happens?

Yes. Black-Scholes prices options off calendar time to expiry, so time value keeps decaying while the market is closed. Long holders pay this Theta overnight and over weekends; sellers collect it.

Why is my Delta different at the open even though the index didn't move?

That is Charm, or Delta decay. As time passes overnight, in-the-money Deltas drift toward one and out-of-the-money Deltas toward zero, so a position that closed balanced can open leaning directional. It is strongest in expiry week.

What is overnight gap risk?

It is the risk of the index opening well away from the prior close on overnight news or global cues. Your gap P&L is roughly your Delta times the gap, but Gamma makes it non-linear, which is why short-option sellers are especially exposed to gaps.

Can implied volatility change while the market is closed?

Effectively yes — IV is re-priced when quoting resumes. Fresh news can open options at higher IV, helping long-Vega holders and hurting sellers, while a passed event can crush IV down at the open, hurting anyone who bought expensive premium.

Is it riskier to hold options over a weekend?

Generally yes. More calendar time passes with the market shut, so Theta and Charm accrue over two or three days, and the window for news to accumulate unhedged is longer. A long weekend before a scheduled event is the highest overnight risk for a premium buyer.

Sources & references

Published 25 April 2026. Educational content only — not investment advice.