diff --git a/src/uu/date/src/date.rs b/src/uu/date/src/date.rs
index c72b1c3048b..82537189c70 100644
--- a/src/uu/date/src/date.rs
+++ b/src/uu/date/src/date.rs
@@ -6,6 +6,7 @@
 // spell-checker:ignore strtime ; (format) DATEFILE MMDDhhmm ; (vars) datetime datetimes getres AWST ACST AEST
 
 mod locale;
+mod system_time;
 
 use clap::{Arg, ArgAction, Command};
 use jiff::fmt::strtime;
@@ -398,22 +399,32 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
 
     // Format all the dates
     for date in dates {
-        match date {
-            // TODO: Switch to lenient formatting.
-            Ok(date) => match strtime::format(format_string, &date) {
-                Ok(s) => println!("{s}"),
-                Err(e) => {
-                    return Err(USimpleError::new(
-                        1,
-                        translate!("date-error-invalid-format", "format" => format_string, "error" => e),
-                    ));
-                }
-            },
-            Err((input, _err)) => show!(USimpleError::new(
-                1,
-                translate!("date-error-invalid-date", "date" => input)
-            )),
+        let date = match date {
+            Ok(date) => date,
+            Err((input, _err)) => {
+                show!(USimpleError::new(
+                    1,
+                    translate!("date-error-invalid-date", "date" => input)
+                ));
+                continue;
+            }
+        };
+
+        #[cfg(unix)]
+        if matches!(settings.format, Format::Custom(_) | Format::Default) {
+            if let Ok(s) = system_time::format_using_strftime(format_string, &date) {
+                println!("{s}");
+                continue;
+            }
         }
+
+        let formatted = strtime::format(format_string, &date).map_err(|e| {
+            USimpleError::new(
+                1,
+                translate!("date-error-invalid-format", "format" => format_string, "error" => e),
+            )
+        })?;
+        println!("{formatted}");
     }
 
     Ok(())
diff --git a/src/uu/date/src/system_time.rs b/src/uu/date/src/system_time.rs
new file mode 100644
index 00000000000..2b47e185f35
--- /dev/null
+++ b/src/uu/date/src/system_time.rs
@@ -0,0 +1,278 @@
+// This file is part of the uutils coreutils package.
+//
+// For the full copyright and license information, please view the LICENSE
+// file that was distributed with this source code.
+
+#[cfg(unix)]
+pub use unix::*;
+
+#[cfg(unix)]
+mod unix {
+    use std::ffi::CString;
+    use std::iter::Peekable;
+    use std::str::Chars;
+
+    use jiff::Zoned;
+    use nix::libc;
+    use uucore::error::{UResult, USimpleError};
+
+    const COLON_Z_FORMATS: [&str; 3] = ["%:z", "%::z", "%:::z"];
+    const COLON_LITERALS: [&str; 3] = ["%:", "%::", "%:::"];
+    const HASH_Z_FORMATS: [&str; 1] = ["%z"];
+    const HASH_LITERALS: [&str; 1] = ["%#"];
+    const STRFTIME_BUF_LEN: usize = 1024;
+
+    struct PrefixSpec<'a> {
+        prefix: char,
+        z_formats: &'a [&'a str],
+        literal_formats: &'a [&'a str],
+    }
+
+    fn is_ethiopian_locale() -> bool {
+        for var in ["LC_ALL", "LC_TIME", "LANG"] {
+            if let Ok(val) = std::env::var(var) {
+                if val.starts_with("am_ET") {
+                    return true;
+                }
+            }
+        }
+        false
+    }
+
+    fn gregorian_to_ethiopian(year: i32, month: i32, day: i32) -> (i32, i32, i32) {
+        let julian_day = julian_day_number(year, month, day);
+        let days_since_epoch = julian_day - 1724221;
+        let (year, day_of_year) = ethiopian_year_and_day(days_since_epoch);
+        let month = day_of_year / 30 + 1;
+        let day = day_of_year % 30 + 1;
+        (year, month, day)
+    }
+
+    fn julian_day_number(year: i32, month: i32, day: i32) -> i32 {
+        let (adj_month, adj_year) = if month <= 2 {
+            (month + 12, year - 1)
+        } else {
+            (month, year)
+        };
+
+        (1461 * (adj_year + 4800)) / 4 + (367 * (adj_month - 2)) / 12
+            - (3 * ((adj_year + 4900) / 100)) / 4
+            + day
+            - 32075
+    }
+
+    fn ethiopian_year_and_day(days_since_epoch: i32) -> (i32, i32) {
+        let cycle = days_since_epoch / 1461;
+        let remainder = days_since_epoch % 1461;
+        let year_in_cycle = remainder / 365;
+        let year_in_cycle = if remainder == 1460 { 3 } else { year_in_cycle };
+        let year = 4 * cycle + year_in_cycle + 1;
+        let day_of_year = remainder - year_in_cycle * 365;
+        (year, day_of_year)
+    }
+
+    fn jiff_format(fmt: &str, date: &Zoned) -> UResult<String> {
+        jiff::fmt::strtime::format(fmt, date).map_err(|e| USimpleError::new(1, e.to_string()))
+    }
+
+    fn format_nanos_padded(nanos: u32) -> String {
+        format!("{nanos:09}")
+    }
+
+    fn format_nanos_trimmed(nanos: u32) -> String {
+        format_nanos_padded(nanos).trim_end_matches('0').to_string()
+    }
+
+    fn nanos_to_u32(nanos: i32) -> UResult<u32> {
+        u32::try_from(nanos).map_err(|_| USimpleError::new(1, "nanoseconds out of range"))
+    }
+
+    fn nanos_from(date: &Zoned) -> UResult<u32> {
+        nanos_to_u32(date.timestamp().subsec_nanosecond())
+    }
+
+    fn format_nanos_for_flag(flag: Option<char>, date: &Zoned) -> UResult<String> {
+        let nanos = nanos_from(date)?;
+        if matches!(flag, Some('-')) {
+            Ok(format_nanos_trimmed(nanos))
+        } else {
+            Ok(format_nanos_padded(nanos))
+        }
+    }
+
+    fn preprocess_format(format: &str, date: &Zoned) -> UResult<String> {
+        let mut output = String::with_capacity(format.len());
+        let mut chars = format.chars().peekable();
+
+        while let Some(c) = chars.next() {
+            if c == '%' {
+                let replacement = rewrite_directive(&mut chars, date)?;
+                output.push_str(&replacement);
+            } else {
+                output.push(c);
+            }
+        }
+
+        Ok(output)
+    }
+
+    fn rewrite_directive(chars: &mut Peekable<Chars<'_>>, date: &Zoned) -> UResult<String> {
+        let Some(next) = chars.next() else {
+            return Ok("%".to_string());
+        };
+
+        match next {
+            'N' => format_nanos_for_flag(None, date),
+            '-' => {
+                let Some(flagged) = chars.next() else {
+                    return Ok("%-".to_string());
+                };
+                if flagged == 'N' {
+                    return format_nanos_for_flag(Some('-'), date);
+                }
+                Ok(format!("%-{flagged}"))
+            }
+            's' => Ok(date.timestamp().as_second().to_string()),
+            'q' => {
+                let q = (date.month() - 1) / 3 + 1;
+                Ok(q.to_string())
+            }
+            'z' => jiff_format("%z", date),
+            '#' => rewrite_prefixed_z(
+                chars,
+                date,
+                PrefixSpec {
+                    prefix: '#',
+                    z_formats: &HASH_Z_FORMATS,
+                    literal_formats: &HASH_LITERALS,
+                },
+            ),
+            ':' => rewrite_prefixed_z(
+                chars,
+                date,
+                PrefixSpec {
+                    prefix: ':',
+                    z_formats: &COLON_Z_FORMATS,
+                    literal_formats: &COLON_LITERALS,
+                },
+            ),
+            '%' => Ok("%%".to_string()),
+            _ => Ok(format!("%{next}")),
+        }
+    }
+
+    fn rewrite_prefixed_z(
+        chars: &mut Peekable<Chars<'_>>,
+        date: &Zoned,
+        spec: PrefixSpec<'_>,
+    ) -> UResult<String> {
+        let max_repeat = spec.z_formats.len();
+        let extra = consume_repeats(chars, spec.prefix, max_repeat.saturating_sub(1));
+        let count = 1 + extra;
+
+        if matches!(chars.peek(), Some(&'z')) {
+            chars.next();
+            return jiff_format(spec.z_formats[count - 1], date);
+        }
+
+        Ok(spec.literal_formats[count - 1].to_string())
+    }
+
+    fn consume_repeats(chars: &mut Peekable<Chars<'_>>, needle: char, max: usize) -> usize {
+        let mut count = 0;
+        while count < max && matches!(chars.peek(), Some(ch) if *ch == needle) {
+            chars.next();
+            count += 1;
+        }
+        count
+    }
+
+    fn calendar_date(date: &Zoned) -> (i32, i32, i32) {
+        if is_ethiopian_locale() {
+            gregorian_to_ethiopian(date.year() as i32, date.month() as i32, date.day() as i32)
+        } else {
+            (date.year() as i32, date.month() as i32, date.day() as i32)
+        }
+    }
+
+    fn build_tm(date: &Zoned) -> libc::tm {
+        let mut tm: libc::tm = unsafe { std::mem::zeroed() };
+
+        tm.tm_sec = date.second() as i32;
+        tm.tm_min = date.minute() as i32;
+        tm.tm_hour = date.hour() as i32;
+
+        let (year, month, day) = calendar_date(date);
+        tm.tm_year = year - 1900;
+        tm.tm_mon = month - 1;
+        tm.tm_mday = day;
+
+        tm.tm_wday = date.weekday().to_sunday_zero_offset() as i32;
+        tm.tm_yday = date.day_of_year() as i32 - 1;
+        tm.tm_isdst = -1;
+
+        tm
+    }
+
+    #[cfg(any(
+        target_os = "linux",
+        target_os = "macos",
+        target_os = "freebsd",
+        target_os = "netbsd",
+        target_os = "openbsd",
+        target_os = "dragonfly"
+    ))]
+    fn set_tm_zone(tm: &mut libc::tm, date: &Zoned) -> Option<CString> {
+        tm.tm_gmtoff = date.offset().seconds() as _;
+
+        let zone_cstring = jiff::fmt::strtime::format("%Z", date)
+            .ok()
+            .and_then(|abbrev| CString::new(abbrev).ok());
+        if let Some(ref zone) = zone_cstring {
+            tm.tm_zone = zone.as_ptr().cast_mut();
+        }
+        zone_cstring
+    }
+
+    #[cfg(not(any(
+        target_os = "linux",
+        target_os = "macos",
+        target_os = "freebsd",
+        target_os = "netbsd",
+        target_os = "openbsd",
+        target_os = "dragonfly"
+    )))]
+    fn set_tm_zone(_tm: &mut libc::tm, _date: &Zoned) -> Option<CString> {
+        None
+    }
+
+    pub fn format_using_strftime(format: &str, date: &Zoned) -> UResult<String> {
+        let format_string = preprocess_format(format, date)?;
+        let mut tm = build_tm(date);
+        let _zone_cstring = set_tm_zone(&mut tm, date);
+        call_strftime(&format_string, &tm)
+    }
+
+    fn call_strftime(format_string: &str, tm: &libc::tm) -> UResult<String> {
+        let format_c = CString::new(format_string)
+            .map_err(|e| USimpleError::new(1, format!("Invalid format string: {e}")))?;
+
+        let mut buffer = vec![0u8; STRFTIME_BUF_LEN];
+        // SAFETY: `format_c` is NUL-terminated, `tm` is a valid libc::tm, and `buffer` is writable.
+        let ret = unsafe {
+            libc::strftime(
+                buffer.as_mut_ptr().cast(),
+                buffer.len(),
+                format_c.as_ptr(),
+                std::ptr::from_ref(tm),
+            )
+        };
+
+        if ret == 0 {
+            return Err(USimpleError::new(1, "strftime failed or result too large"));
+        }
+
+        let len = ret as usize;
+        Ok(String::from_utf8_lossy(&buffer[..len]).into_owned())
+    }
+}
diff --git a/tests/by-util/test_date.rs b/tests/by-util/test_date.rs
index 9a98b1b0309..e841a2e3d67 100644
--- a/tests/by-util/test_date.rs
+++ b/tests/by-util/test_date.rs
@@ -476,6 +476,13 @@ fn test_date_set_valid_4() {
 }
 
 #[test]
+#[cfg(unix)]
+fn test_invalid_format_string() {
+    new_ucmd!().arg("+%!").succeeds().stdout_is("!\n");
+}
+
+#[test]
+#[cfg(not(unix))]
 fn test_invalid_format_string() {
     let result = new_ucmd!().arg("+%!").fails();
     result.no_stdout();
@@ -1132,6 +1139,85 @@ fn test_date_military_timezone_with_offset_variations() {
     }
 }
 
+#[cfg(unix)]
+fn ethiopian_locale_available() -> bool {
+    let output = std::process::Command::new("locale")
+        .env("LC_ALL", "am_ET.UTF-8")
+        .arg("charmap")
+        .output();
+    let Ok(output) = output else {
+        return false;
+    };
+    if !output.status.success() {
+        return false;
+    }
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    stdout.trim() == "UTF-8"
+}
+
+#[test]
+#[cfg(unix)]
+fn test_date_ethiopian_calendar_locale() {
+    if !ethiopian_locale_available() {
+        return;
+    }
+
+    let current_year: i32 = new_ucmd!()
+        .env("LC_ALL", "C")
+        .arg("+%Y")
+        .succeeds()
+        .stdout_str()
+        .trim()
+        .parse()
+        .unwrap();
+
+    let year_september_10: i32 = new_ucmd!()
+        .env("LC_ALL", "am_ET.UTF-8")
+        .arg("-d")
+        .arg(format!("{current_year}-09-10"))
+        .arg("+%Y")
+        .succeeds()
+        .stdout_str()
+        .trim()
+        .parse()
+        .unwrap();
+
+    let year_september_12: i32 = new_ucmd!()
+        .env("LC_ALL", "am_ET.UTF-8")
+        .arg("-d")
+        .arg(format!("{current_year}-09-12"))
+        .arg("+%Y")
+        .succeeds()
+        .stdout_str()
+        .trim()
+        .parse()
+        .unwrap();
+
+    assert_eq!(year_september_10, year_september_12 - 1);
+    assert_eq!(year_september_10, current_year - 8);
+    assert_eq!(year_september_12, current_year - 7);
+
+    let iso_hours = new_ucmd!()
+        .env("LC_ALL", "am_ET.UTF-8")
+        .arg("--iso-8601=hours")
+        .succeeds()
+        .stdout_str();
+    assert!(
+        iso_hours.starts_with(&format!("{current_year}-")),
+        "--iso-8601 should use Gregorian year, got: {iso_hours}"
+    );
+
+    let rfc_date = new_ucmd!()
+        .env("LC_ALL", "am_ET.UTF-8")
+        .arg("--rfc-3339=date")
+        .succeeds()
+        .stdout_str();
+    assert!(
+        rfc_date.starts_with(&format!("{current_year}-")),
+        "--rfc-3339 should use Gregorian year, got: {rfc_date}"
+    );
+}
+
 // Locale-aware hour formatting tests
 #[test]
 #[cfg(unix)]