Is DTE calendar days or trading days?

Calendar days, unless the UI says otherwise.

Do shorter expirations always decay faster?

Yes in percentage terms near the money; the dollar amount of decay depends on the option.

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Concept guide

Days to Expiration (DTE)

DTE is the number of calendar days between today and an option's expiration date.

Concept

Why DTE matters

DTE sets both the time available for a thesis and the rate of time decay. Shorter DTE means faster decay and a smaller expected move; longer DTE costs more but decays more slowly in percentage terms.

Choosing an expiration

Short-dated options suit precise, near-term views and income but leave little room to manage. Longer-dated options suit open-ended theses and hedges but tie up more capital.

Credit strategies often use 30–45 DTE to balance decay and management room.
Event trades must choose an expiration that actually contains the event.
Very short DTE raises pin and assignment risk.

FAQ

Is DTE calendar days or trading days?: Calendar days, unless the UI says otherwise.
Do shorter expirations always decay faster?: Yes in percentage terms near the money; the dollar amount of decay depends on the option.