BenKitTimezone / Date Simulator.
One instant, wherever your app runs. Catch date boundaries and clock changes before they become bugs.
Set the moment
INPUT / 01Try an edge case
Start from a timestamp
This is a test-data simulator. It doesn’t change your device clock or another app’s timezone.
±24h moves elapsed time. +1 day follows the source calendar and may span 23 or 25 hours at DST.
Copy manually
Test the date your users actually see.
An API timestamp is one instant. Its calendar date depends on the timezone. Use this simulator when checking daily streaks, reminders, subscription boundaries, or date labels in an app.
- Enter a wall-clock date and its source timezone, or load an exact timestamp.
- Compare the same instant in UTC and your users’ timezones.
- Try midnight, leap day, and daylight saving presets. Copy the test JSON into your fixtures.
A few things worth knowing
Does this change my app or device clock?
No. It generates test inputs and expected timezone representations. Inject these values into your app’s clock abstraction or test fixtures. Device-level testing requires your platform’s own testing tools.
What is the difference between UTC and local time?
UTC identifies the shared reference time. Local time is that instant represented using a timezone’s rules. A fixed offset such as +08:00 is not the same as an IANA timezone, which may include historical and daylight saving changes.
How are skipped and repeated times handled?
The default is to flag them rather than silently adjust. During a skipped hour, an earlier or later choice shifts by the clock-change gap. During a repeated hour, it chooses the first or second occurrence. The simulator explains the applied resolution.
Where do the timezone rules come from?
Calculations use Temporal and your browser’s timezone data. Government rule changes may reach older browsers late. Dates use the ISO / Gregorian calendar; leap seconds are not modeled.
Are my test dates uploaded?
No. Calculations happen in this page. There is no account, date storage, or server-side processing of your inputs.