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Bun supports programmatically setting a default time zone for the lifetime of the bun process. To do set, set the value of the TZ environment variable to a valid timezone identifier.

When running a file with bun, the timezone defaults to your system’s configured local time zone.When running tests with bun test, the timezone is set to UTC to make tests more deterministic.

process.ts

process.env.TZ = "America/New_York";

Alternatively, this can be set from the command line when running a Bun command.

terminal

TZ=America/New_York bun run dev

Once TZ is set, any Date instances will have that time zone. By default all dates use your system’s configured time zone.

process.ts

new Date().getHours(); // => 18

process.env.TZ = "America/New_York";

new Date().getHours(); // => 21

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