---
title: "Theta & Time Decay"
type: "lesson"
topic: "Futures & Options (Indian markets)"
level: "Intermediate"
read_minutes: 7
slug: "theta-decay"
url: "https://learn-derivatives.tapetide.com/learn/theta-decay"
markdown_url: "https://learn-derivatives.tapetide.com/learn/theta-decay.md"
source: "DeltaDesk by Tapetide"
license: "Educational use — attribute DeltaDesk (Tapetide)"
---

# Theta & Time Decay

> **In plain English:** An option is like an ice cube — it melts a little every day, and melts fastest right before it disappears (expiry). If you bought it, that melting costs you money. If you sold it, the melting is your profit. The catch: a sudden market move can hurt the seller faster than the melting helps.

Time decay is the closest thing options trading has to gravity. Every day that passes, an option loses a little time value — and that loss accelerates as expiry nears.

## The decay curve is not a straight line

An option’s time value does not bleed away evenly. It decays slowly when far from expiry and then drops off a cliff in the final days — roughly proportional to the square root of time remaining. A weekly option loses most of its time value in its last two or three days.

## Why sellers love the last week

Because decay accelerates, option sellers often focus on the final days before expiry, when theta is richest. This is the engine behind weekly expiry selling on NIFTY and BANKNIFTY. The catch: gamma is also highest then, so a sudden move can wipe out weeks of collected theta in minutes.

> **Warning:** Theta and gamma are a trade-off. The premium you collect for time decay is exactly the compensation for the gamma risk of a sharp move. There is no free theta.

## Theta is not realised until it is

A common beginner error is treating theta as guaranteed daily income. It is only realised if the underlying behaves. A theta-positive position that gets run over by a big move can lose far more than a week of decay. Always size for the bad day, not the average day.

> **Key takeaway:** Key takeaway: time value decays fastest near expiry. Sellers harvest it but pay for it in gamma risk.

---

**Learn this interactively at [DeltaDesk](https://learn-derivatives.tapetide.com/learn/theta-decay)** — payoff builders, live Greeks and real NSE data.

*Educational content only — nothing here is investment advice. Derivatives carry significant risk of loss. Tapetide is not a SEBI-registered research analyst or investment adviser.*