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Gamma vs theta: why short expiries pay more and bite harder

Theta is what a seller earns each day from time passing. Gamma is how fast a stock move changes the risk. As expiry gets close, both grow at the same time, so the last few days pay the most per day and can lose a week of decay on one small move.

Comparison · 7-minute read · Updated 2026-11-09

The short answer

Theta is how much an option loses in value each day, all else equal. When you sell an option, that decay is money moving toward you. It's the "rent" a seller collects.

Gamma is how fast Delta changes when the stock moves $1. In plain words, it's how quickly a small move turns into a big one. For a seller, high gamma means losses speed up as the stock moves against you.

They're two sides of one deal. You can't get big daily theta without taking big gamma. Near expiry, both climb together. That's why short-dated options pay the most per day and why they can wipe out a week of gains in a single afternoon.

Side by side

One short put, three expiries (hypothetical)

Birchfield Motors, a made-up stock, trades at $100. Implied volatility is 30%. You sell the $100 put, right at the money. We look at the same put with 45, 21 and 3 days left. All prices are Black-Scholes model values per contract, with a 4% interest rate.

Read the rows top to bottom.

Theta grows. At 45 days, time pays you about $4 a day. At 3 days, about $18 a day. More than four times as fast. That's the pull of short expiries.

Gamma grows faster. At 3 days, gamma is about four times what it was at 45. Same strike, same stock. The option's risk now changes much more for each dollar the stock moves.

So the same move hurts more. A $2 drop costs $100 at 45 days and $126 at 3 days. A $4 drop costs $215 at 45 days and $298 at 3 days. The gap widens with every extra dollar. That's gamma at work.

The 3-day row: a week of theta, gone

At 3 days, you're earning $18 a day. A $2 drop costs $126. That's seven days of theta, and there are only three days left. You can't earn it back by waiting.

Here's how fast the risk shifts. With 3 days left, the put's delta is about 0.49. After that $2 drop, it jumps to about 0.76. Now each further $1 down costs you about $76, not $49. If Birchfield ends at $96, the put is worth $4 at expiry. You collected $1.07. That's −$293.

Compare the 45-day put. The same $2 drop costs $100, but you have 45 days of theta to help, and the delta moves from 0.46 to only about 0.54. Slower, calmer, more time to decide.

How sellers handle the trade-off

You don't have to pick theta or gamma. You pick where on the curve you sit.

• More time (30 to 45 days). Less theta per day, much less gamma. Moves hurt less and you have room to roll. This is where many sellers open trades.
• Less time (under a week). The most theta per day, and the most gamma. A small move decides the trade. 0DTE vs weekly options covers this end.
• Close before the last days. Many sellers take profits or roll with a week or two left. They skip the stretch where gamma is highest for the last few dollars of premium.

In the wheel strategy, a gamma surprise near expiry usually means assignment. Fine if you wanted the shares, painful if you sized too big.

Gamma also explains why a short straddle feels so violent near expiry. Short straddle vs iron butterfly shows what wings do to that risk. And when earnings land inside a trade, a third force joins in. IV crush vs theta decay splits the two apart in dollars. To see every strategy side by side, use the options strategy comparison chart.

The theta decay calculator shows how the daily decay changes as expiry gets close.

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