Home › Guides › Options: the math

Theta for option sellers: how time decay pays you

Theta is how much an option's price melts each day if nothing else changes. Sellers like it because that melt is the pay for waiting. It isn't even, though, and the fast part comes with a cost.

Options guide · 8-minute read · Updated 2026-10-27

The short answer

Theta is the amount an option's price drops each day from time passing alone. If a put has a theta of −0.03, it loses about 3 cents a day, all else equal.

An option buyer pays theta. An option seller collects it. That's why sellers say they get "paid to wait." The catch is that theta speeds up near expiry, and so does the risk of a sharp move against you.

What actually decays

Only the time value melts. That's the Extrinsic value part of the premium. Intrinsic value doesn't decay at all.

So theta is biggest on options at or near the money, where the whole premium is time value. It's small on options far out of the money (there's little to melt) and on options deep in the money (most of the price is intrinsic). Intrinsic vs extrinsic value for sellers has the split.

The decay curve, from 45 days to zero

A made-up stock, XYZ, trades at $50. Take a $50 put and assume the stock and Implied volatility (30%) never change. These are rough model prices (an illustration, not a trade idea).

Look at the shape. The first 24 days melt 30% of the price. The last 21 days melt the other 70%. Time value shrinks roughly with the square root of time left, so the melt keeps speeding up.

Why sellers like the 45-to-21 window

Many sellers open around 30 to 45 days and close or roll near 21 days. Here's the thinking.

• At 45 days, decay is slow but steady, and the option's price doesn't jump much when the stock moves.
• Near 21 days, you've often collected a good share of the premium.
• After 21 days, decay is fastest, but so is gamma: the option's price starts reacting hard to every dollar the stock moves. See gamma risk for option sellers.

That's a habit many sellers use, not a rule. 30 DTE vs 45 DTE compares the two most common starting points.

The worked example, closed at 21 days

You sell the 45-day $50 put for $2.00 and collect $200. You plan to buy it back at 21 days. Here's what that looks like, with rough model prices.

This is the honest picture of theta. It works every day the stock behaves. It's easily outweighed by one day that doesn't.

What makes theta bigger or smaller

Notice that every row that makes theta bigger also raises your risk. Closer strikes get tested more. High IV means bigger expected moves. Short expiries move fast.

How theta fits the wheel

In the wheel strategy, theta is the reason you sell instead of buy. Each cash-secured put and each covered call is a trade where time works for you.

But theta never pays for a bad stock. If XYZ falls 20%, no amount of daily melt covers it. Pick the stock first, then let theta do its part.

Try it today (no money needed)

1. Open the Options chain for a stock you know. Find the at-the-money put about 45 days out. Write down its price and theta.
2. Find the same strike at about 21 days and 7 days out. Note price and theta for each.
3. Divide price by days left for each. Watch the per-day number climb.
4. Paper-trade the 45-day put. Check it at 21 days. How much did time pay, and how much did the stock move it?
5. Read theta decay explained for the buyer's side of the same curve.

Questions