Theta measures how much an option’s price is expected to change as one unit of time passes, assuming other factors hold constant. For 0DTE options, that “unit of time” is no longer days or weeks — it is hours and minutes.
The Shape of Time Decay
For longer-dated options, time decay is relatively slow at first. The loss of extrinsic value accelerates as expiration approaches. If you plotted remaining time value versus time, the curve would be shallow at the start and steep near the end.
0DTE options live entirely in that last, steep part of the curve. This is why they can lose value quickly when price drifts, and gain value suddenly when price moves sharply.
Practical Consequences for 0DTE Traders
- Premium sellers benefit when time passes and price stays within a manageable range — but are exposed to sharp moves.
- Premium buyers pay for the possibility of intraday moves, and time works against them every minute price is quiet.
- Close to the close, even small changes in price can have large percentage effects on remaining time value.
Why the Last Hour is Different
In the last hour, the option market stops pricing “what might happen tomorrow” and focuses entirely on “where will we settle today.” Market makers update quotes quickly as underlying price and order flow change, and theta decay can feel almost discontinuous.
Understanding the shape of the theta curve helps frame which parts of the session you want to be active in — and which parts you prefer to avoid.