Input
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How to use
- Enter the source date, time and time zone.
- Choose comparison zones or add more cards.
- Shift or swap times as needed, then copy a card or download JSON.
One instant across time zones
A local clock time needs a time zone to identify an instant. Once that instant is known, comparison cities can show different dates and clock times without representing different moments.
Named zones account for date-dependent offset rules. A fixed UTC offset describes a simpler offset and does not carry a region’s daylight-saving schedule.
Comparison cards
Each card represents the source instant in its selected zone. Adding a card does not create a separate source time; swapping a card with the source preserves the instant while changing how it is entered.
2026-01-01 09:00:00 · UTC → Asia/Tokyo2026-01-01T18:00:00+09:00[Asia/Tokyo]A fixed example; the time zone and precision are part of the calculation.
Daylight-saving transitions
A local time may be missing when clocks move forward or occur twice when they move back. The default rejects such ambiguity; choose Earlier, Later or Compatible deliberately when resolving it.
Copying a zone value
A card’s Copy action includes its date, time, offset and zone name. Download saves the comparison as JSON. Keep the date when sharing a time near midnight, because another zone may fall on the previous or next day.
ISO calendar dates, nanosecond precision and explicit time zones. Cron uses five fields, up to 50 runs within 10 years, reference years 1900–2199 and a 5-second processing limit. Time-zone data comes from your browser. Processing stays on your device.
Frequently asked questions
Can the target date be different?
Yes. The same instant can fall on a different calendar date in another zone. Read both the date and time on each card.
Can I use a fixed UTC offset?
Yes. A fixed offset has no seasonal transition rules; use a named IANA zone when regional daylight-saving behavior matters.
Why is a local clock time rejected?
It may be missing or repeated during a clock transition. Check the date and zone, then choose a resolution if that ambiguity is intentional.
Does Swap preserve the instant?
Yes. It makes the selected comparison zone the source and moves the old source zone into that card, keeping the represented moment.
Where do the time-zone rules come from?
The runtime supplies the zone data. Different browser or runtime data versions can produce differences for changed historical or future rules.