R Warning Message in as.POSIXct.POSIXlt(x) : unknown timezone (2 Examples)

On this page, I’ll illustrate how to reproduce and fix the “Warning Message in as.POSIXct.POSIXlt(x) : unknown timezone” in R.

Example 1: Replicating the Unknown Timezone Warning Message in as.POSIXct.POSIXlt(x)

as.POSIXct("2025-01-01",        # Wrong timezone name
           tz = "CT")
# [1] "2025-01-01"
# In as.POSIXct.POSIXlt(x) : unknown timezone 'CT'

Example 2: Debugging the Unknown Timezone Warning Message in as.POSIXct.POSIXlt(x)

as.POSIXct("2025-01-01",        # Set to own timezone
           tz = Sys.timezone())
# [1] "2025-01-01 UTC"

Further Resources & Related Articles

In addition, you may want to read some of the other articles on this website. I have published several tutorials already.

• How to Avoid R Warning Message – NAs Introduced by Coercion
• Warning Message – Removed rows containing non-finite values (stat_bin)
• ggplot2 Warning Message in R – Use of Data is discouraged
• Warning Message in R – cor() standard deviation is zero