Can a zone show more than two transitions in a single year?

Rarely, but yes. If the zone's own government changed its daylight saving rules during the checked range, a historical rule change can add extra transitions beyond the usual spring and fall pair.

Why does a zone like Arizona show zero transitions at all?

Because that zone does not observe daylight saving time in the first place, so its offset never changes across the year and there is nothing to detect.

DST Transition Comparator

Pick a zone and a date range. See every date the zone's UTC offset changes, and what it changes from and to.

Just need the difference between two zones on one date? See Time Zone Difference Calculator.

Want to learn more?

How Daylight Saving Transitions Distort Elapsed-Time Math

Worked example

America/New_York shows exactly one transition in March 2027, a spring-forward move from UTC minus 5 to UTC minus 4, and another in November when it falls back the other direction. America/Phoenix, checked across that same full year, shows zero transitions at all, since Arizona does not observe daylight saving time and its offset simply never changes. Comparing two zones side by side this way makes the real difference between a DST-observing zone and a fixed-offset zone visible directly, rather than something you have to already know in advance before trusting a calculation that spans either zone.

Common mistakes

Assuming every time zone observes daylight saving. Many do not, and a genuine zero-transition result for a full year is a correct, expected outcome for those zones, not a sign of a missed detection.
Checking a range far shorter than a full year and concluding a zone has fewer transitions than it actually does over a complete annual cycle.

Limitations

Detection compares each day's local-noon offset to the previous day's, which finds every real transition date but does not pinpoint the exact hour within that day the change actually took effect. The checked range is bounded to roughly 800 days.

Frequently asked questions

Can a zone show more than two transitions in a single year?: Rarely, but yes. If the zone's own government changed its daylight saving rules during the checked range, a historical rule change can add extra transitions beyond the usual spring and fall pair.
Why does a zone like Arizona show zero transitions at all?: Because that zone does not observe daylight saving time in the first place, so its offset never changes across the year and there is nothing to detect.