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Why Theta Decay Matters on 0DTE and 1DTE Options

Theta is the options Greek that estimates how much value time takes out of a contract. On 0DTE and 1DTE that cost is crowded into a few hours.

By Hunter (Orion). March 8, 2026. 8 min read.

Short answer: Theta is the options Greek that estimates how much value time takes out of a contract. On 0DTE and 1DTE options that cost is crowded into a few hours. A move in the direction you wanted can still leave the contract flat, because time is working against a long option the whole way. This page is a definition and a hypothetical example. It is not a trade record and it is not a recommendation.

What theta measures

An option price has more than direction in it. Part of the premium is time. Theta is the model estimate of how much that time value changes as the clock runs, usually quoted as a change per day.

A few things follow from that definition.

Theta is an estimate from a pricing model. It is not a bill the exchange sends you.
For a long call or a long put, theta is a cost. You paid for time, and the remaining time gets shorter.
For a short option, the same number is a credit in the model. That is a description of the sign, not a suggestion to sell options.
The number on the chain can change when price, volatility, or the clock changes. A theta you read at the open is not a promise about the close.

People sometimes treat the premium as "the cost of being right on direction." On a long-dated option, time is a small slice of the day. On a contract that expires today or tomorrow, time is a large slice of what you paid.

Why the last day is different

Time value does not come out in equal pieces. A contract with 40 days left can lose a little time value each day and still have most of the premium left. A contract with one day left has to shed the remaining time value before expiration. A 0DTE contract has even less clock. There is no overnight session left in the contract. Whatever time value is still in the premium has to come out before the close, unless the contract finishes in the money enough to keep intrinsic value.

That is why a favorable move and a higher mark are not the same sentence.

Direction can lift the option. Volatility can lift it or crush it. Theta, for a long option, is the piece pulling the other way. If the directional piece is smaller than the time piece, the mark can fall while the index rises. The index "going your way" is not the option's profit and loss.

None of this says a same-day option is good or bad. It says the clock is one of the inputs, and on the last day it is a large one.

A hypothetical 1DTE call

This walk-through uses round numbers so the arithmetic is easy. The prices are made up. It is not a trade anyone took.

A 1DTE call is marked at 5.00. The model shows theta of 0.35.
The options multiplier is 100. A theta of 0.35 is an estimate of about $35 of time decay per contract for that day, if price and volatility do not change. 0.35 times 100 is 35.
Later, the index is higher and the same call is marked at 5.20.
The mark is 0.20 above where it started. Direction helped. Time was a cost the whole time, and the model had put that cost near 0.35 for the day.
If the directional lift had been smaller than the time cost, the mark could have been below 5.00 even though the index rose.

Read step 5 again before turning it into a rule. The 0.20 and the 0.35 are not a forecast. They are a picture of two forces that do not have to agree. A real contract also moves when implied volatility changes. Theta is not the only Greek in the mark.

What this example does not say

It does not say the next 1DTE call will behave like the numbers above.
It does not say a certain percent gain is the right place to get out.
It does not say selling options is the fix. The sign of theta flips for a short option, and so does the risk. A short option can lose more than the credit you received.
It does not describe a trade Hunter took, or a result from any account.

If you want a hold rule, write it before you enter, for that contract, with the theta the model is showing then. A rule copied from someone else's example is just their number.

Checks before you hold into the last hours

These are questions, not a system.

What is the theta on this contract right now? Read it. Remember it is an estimate.
What move would you need for direction to matter more than that estimate? If you cannot say it in points or in premium, you do not have a plan yet.
Is this 0DTE or 1DTE? A 0DTE contract does not have a tomorrow inside the expiration. A 1DTE contract still has the overnight clock.
What else is in the mark? A volatility crush can dwarf theta. A volatility expansion can hide it. Theta is one line on the card.
How much cash is the premium? On a long option, the premium debit is the most you can lose on that contract, before fees. Size that debit against the account before you debate the hold.

The last point is the one people skip. A small theta argument on a huge position is still a huge position.

FAQ

Does a higher index always mean a higher call?

No. The call price also includes time and volatility. On 0DTE and 1DTE contracts, the time piece is large relative to the life of the option. The index can rise and the call can still be unchanged or lower.

Is theta the same every hour?

No. The daily theta figure is a model summary. The decay is not a straight line through the day, and it is not the same at every strike. At-the-money contracts usually carry more time value than contracts that are far from the index.

Should you sell options so theta pays you?

This page does not say that. Short options have the opposite theta sign and a different loss profile. A credit is not a result. Read the risk disclosure before you treat any Greek as a plan.

Where Zero-G fits

If you want to see the cash at risk on a premium before you size it, the 0DTE risk calculator takes a premium, a contract count, and an account size and shows the debit. It does not forecast where the contract will be later. You still decide whether the position belongs in the account.

For the written risk language that covers this whole site, read the risk disclosure.