lubridate with_tz() in R: Convert Time Zones for Display

The lubridate with_tz() function shows a date-time in a different time zone without changing the actual moment in time it represents. It re-labels the clock for display while the underlying instant stays exactly the same.

with_tz(t, "America/New_York")        # display in New York
with_tz(t, "Asia/Tokyo")              # display in Tokyo
with_tz(t, "Europe/London")           # display in London
with_tz(t, "UTC")                     # display in UTC
with_tz(t)                            # display in system tz
with_tz(t, tzone = Sys.timezone())    # explicit system tz
with_tz(now(), "Australia/Sydney")    # current time elsewhere

What with_tz() does in one sentence

with_tz(time, tzone) returns the same instant displayed under a different time zone. The number of seconds since the epoch is untouched; only the calendar and clock labels used to print the value change.

A date-time in R is an absolute moment, like "the instant 1.7 billion seconds after 1970". That moment can be described as 12:00 in London or 07:00 in New York, and both descriptions point to the identical event. with_tz() swaps which description you see.

Syntax

with_tz(time, tzone = "", ...). time is a POSIXct date-time; tzone is an Olson time zone name string; an empty string means the system time zone.

The input must already carry a correct time zone. with_tz() reads that zone, converts to the requested tzone, and prints the result. It never guesses what zone your data came from.

Convert between time zones

1. Display a UTC timestamp locally

One UTC instant becomes three readings. New York is five hours behind, Tokyo nine ahead, and Sydney eleven ahead because January falls in its daylight saving period. The event is one moment; only the display differs.

2. Convert between two non-UTC zones

with_tz() works from any source zone, not just UTC. A 9 AM New York meeting in June shows as 2 PM in London, and lubridate applies each zone's daylight saving rules automatically.

3. Vectorized conversion

with_tz() is vectorized. Note the offset changes within the vector: January prints EST at UTC-5, July prints EDT at UTC-4, because the conversion respects daylight saving on a per-element basis.

4. Current time in another city

Pair with_tz() with now() to answer "what time is it there right now". The output above is illustrative; the live value depends on when the code runs.

with_tz() vs force_tz()

These two functions look alike but do opposite jobs. with_tz() preserves the instant and re-labels the clock, while force_tz() preserves the clock and re-labels the instant.

Decision rule. Use with_tz() when the timestamp is correct and you only want to read it in another city. Use force_tz() when the timestamp was parsed with the wrong zone, for example data stored as local time that lubridate assumed was UTC.

Common pitfalls

Three traps catch most users. First, a string parsed without tz = is assumed to be UTC, so the conversion starts from the wrong zone; pass tz to ymd_hms() or use force_tz(). Second, an unrecognized zone name warns and leaves the value unchanged, so always use full Olson names such as "America/New_York" rather than "New York" or "EST". Third, a plain Date has no time component, so converting it invents a midnight that then shifts across the date line.

Try it yourself

Related lubridate functions

• force_tz(): keeps the clock reading and changes the instant, the opposite of with_tz().
• tz(): returns the time zone string currently attached to a date-time.
• now(): current date-time as a POSIXct, ready to pass to with_tz().
• ymd_hms(), mdy_hms(), dmy_hms(): parse date-time strings with a tz argument.
• as_date(): drop the time component and return a plain Date.

FAQ

What is the difference between with_tz() and force_tz() in R?

with_tz() keeps the underlying instant fixed and changes how it is displayed, so a UTC noon becomes a New York 7 AM that points to the same moment. force_tz() keeps the clock reading fixed and changes the instant, so a UTC noon becomes a New York noon that is a different moment five hours later. Use with_tz() to view a correct timestamp elsewhere, and force_tz() to correct a timestamp parsed in the wrong zone.

Does with_tz() change the actual time?

No. with_tz() never alters the moment a date-time represents. If you compare a value before and after with_tz(), R reports them as equal because they are the same point on the timeline. Only the time zone label and the printed clock and calendar values change. This is why with_tz() is safe to use right before printing or plotting without affecting any arithmetic.

How do I convert UTC to local time in R?

Parse or store the timestamp with tz = "UTC", then call with_tz() with your local Olson zone name. For example, with_tz(ymd_hms("2024-01-15 12:00:00", tz = "UTC"), "America/Chicago"). To use the machine's own zone, call with_tz(t) with no second argument, or pass tzone = Sys.timezone() to be explicit about the target zone.

What time zone names does with_tz() accept?

with_tz() accepts Olson (IANA) time zone names such as "America/New_York", "Europe/London", and "Asia/Tokyo". Run OlsonNames() to list every value your R installation supports. Avoid short abbreviations like "EST" or "PST", because they are ambiguous, ignore daylight saving, and may trigger a warning or silently fall back to UTC.

Can with_tz() handle a vector of date-times?

Yes. with_tz() is vectorized and converts every element of a POSIXct vector in one call. Each element is converted independently, so a vector spanning winter and summer correctly shows different UTC offsets per element as daylight saving turns on and off. The result is a single POSIXct vector carrying the requested time zone.