diff --git a/src/time/parser.rs b/src/time/parser.rs
index 96f6125..b2aa60f 100644
--- a/src/time/parser.rs
+++ b/src/time/parser.rs
@@ -1,5 +1,5 @@
 //! Implements a parser for ISO-8601 format Time
-use super::{DateTime, Error, TimeZone};
+use super::{DateTime, Error, Sign, TimeZone, Offset};
 
 #[derive(Debug, PartialEq)]
 enum Format {
@@ -53,6 +53,26 @@ impl<'a> Parser<'a> {
         }
     }
 
+    fn validate_day(&self, day: u8) -> Result<(), Error> {
+        let max = match self.month {
+            Some(1|3|5|7|10|12) => 31,
+            Some(2) => {
+                if self.year.unwrap() % 4 == 0 {
+                    29
+                } else {
+                    28
+                }
+            },
+            Some(4|6|9|11) => 30,
+            _ => return Err(Error::InvalidMonth),
+        };
+        if day > max {
+            Err(Error::InvalidDay)
+        } else {
+            Ok(())
+        }
+    }
+
     fn number(&mut self, c: char) -> Result<(), Error> {
         self.buffer.push(c);
         match self.mode {
@@ -67,6 +87,9 @@ impl<'a> Parser<'a> {
             Mode::Month => {
                 if self.buffer.len() == 2 {
                     let m: u8 = self.buffer.parse()?;
+                    if m > 12 {
+                        return Err(Error::InvalidMonth);
+                    }
                     self.buffer.clear();
                     self.month = Some(m);
                     self.mode = Mode::Day;
@@ -76,6 +99,7 @@ impl<'a> Parser<'a> {
             Mode::Day => {
                 if self.buffer.len() == 2 {
                     let d: u8 = self.buffer.parse()?;
+                    self.validate_day(d)?;
                     self.buffer.clear();
                     self.day = Some(d);
                     self.mode = Mode::Hour;
@@ -87,6 +111,9 @@ impl<'a> Parser<'a> {
             Mode::Hour => {
                 if self.buffer.len() == 2 {
                     let h: u8 = self.buffer.parse()?;
+                    if h > 23 {
+                        return Err(Error::InvalidHour);
+                    }
                     self.buffer.clear();
                     self.hour = Some(h);
                     self.mode = Mode::Minute;
@@ -98,6 +125,9 @@ impl<'a> Parser<'a> {
             Mode::Minute => {
                 if self.buffer.len() == 2 {
                     let m = self.buffer.parse()?;
+                    if m > 59 {
+                        return Err(Error::InvalidMinute);
+                    }
                     self.buffer.clear();
                     self.minute = Some(m);
                     self.mode = Mode::Second;
@@ -109,6 +139,9 @@ impl<'a> Parser<'a> {
             Mode::Second => {
                 if self.buffer.len() == 2 {
                     let s = self.buffer.parse()?;
+                    if s > 59 {
+                        return Err(Error::InvalidSecond);
+                    }
                     self.buffer.clear();
                     self.second = Some(s);
                     self.mode = Mode::TimeZone;
@@ -136,7 +169,7 @@ impl<'a> Parser<'a> {
         Ok(())
     }
 
-    fn dash(&mut self, c: char) -> Result<(), Error> {
+    fn dash(&mut self) -> Result<(), Error> {
         match self.mode {
             Mode::Year => return Err(Error::UnexpectedChar(Mode::Year, '-')),
             Mode::Month => {
@@ -174,7 +207,7 @@ impl<'a> Parser<'a> {
         Ok(())
     }
 
-    fn colon(&mut self, c: char) -> Result<(), Error> {
+    fn colon(&mut self) -> Result<(), Error> {
         match self.mode {
             Mode::Year | Mode::Month | Mode::Day => return Err(Error::UnexpectedChar(self.mode, ':')),
             Mode::Hour | Mode::Minute | Mode::Second => {
@@ -196,7 +229,7 @@ impl<'a> Parser<'a> {
         Ok(())
     }
 
-    fn tee(&mut self, c: char) -> Result<(), Error> {
+    fn tee(&mut self) -> Result<(), Error> {
         if self.mode != Mode::Hour || !self.buffer.is_empty() {
             Err(Error::UnexpectedChar(self.mode, 'T'))
         } else {
@@ -205,7 +238,7 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn zed(&mut self, c: char) -> Result<(), Error> {
+    fn zed(&mut self) -> Result<(), Error> {
         if self.mode == Mode::Year || !self.buffer.is_empty() {
             return Err(Error::UnexpectedChar(self.mode, 'Z'));
         } else {
@@ -216,7 +249,26 @@ impl<'a> Parser<'a> {
     }
 
     fn parse_tz_basic(&mut self) -> Result<(), Error> {
-        todo!()
+        let sign = match self.buffer.chars().next() {
+            Some('+') => Sign::Positive,
+            Some('-') => Sign::Negative,
+            _ => return Err(Error::InvalidOffset),
+        };
+        let Some(n) = self.buffer.get(1..3) else {
+            return Err(Error::InvalidOffset);
+        };
+        let hours: u8 = n.parse()?;
+        let minutes: Option<u8> = if let Some(n) = self.buffer.get(3..) {
+            Some(n.parse()?)
+        } else {
+            None
+        };
+        match (hours, minutes) {
+            (h, None) if h > 12 => return Err(Error::InvalidOffset),
+            (h, Some(m)) if h == 12 && m > 0 || m > 59 => return Err(Error::InvalidOffset),
+            _ => self.tz = Some(TimeZone::Offset(Offset { sign, hours, minutes })),
+        }
+        Ok(())
     }
 
     fn parse_tz_extended(&mut self) -> Result<(), Error> {
@@ -231,10 +283,10 @@ impl<'a> Parser<'a> {
         for c in self.text.chars() {
             match c {
                 x if x.is_numeric() => self.number(c)?,
-                '-' => self.dash(c)?,
-                ':' => self.colon(c)?,
-                'T' => self.tee(c)?,
-                'Z' => self.zed(c)?,
+                '-' => self.dash()?,
+                ':' => self.colon()?,
+                'T' => self.tee()?,
+                'Z' => self.zed()?,
                 _ => return Err(Error::UnexpectedChar(self.mode, c)),
             }
         }
@@ -243,9 +295,11 @@ impl<'a> Parser<'a> {
                 if self.tz == Some(TimeZone::UTC) && !self.buffer.is_empty() {
                     return Err(Error::TrailingGarbage);
                 }
-                match self.format {
-                    Format::Basic => self.parse_tz_basic()?,
-                    Format::Extended => self.parse_tz_extended()?,
+                if self.tz.is_none() {
+                    match self.format {
+                        Format::Basic => self.parse_tz_basic()?,
+                        Format::Extended => self.parse_tz_extended()?,
+                    }
                 }
             },
             _ => return Err(Error::Truncated),
@@ -261,3 +315,22 @@ impl<'a> Parser<'a> {
         })
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn parse_full_utc() {
+        let parser = Parser::new("2023-05-09T19:39:15Z");
+        let dt = parser.parse().unwrap();
+        assert_eq!(dt.year, 2023);
+        assert_eq!(dt.month, Some(5));
+        assert_eq!(dt.day, Some(9));
+        assert_eq!(dt.hour, Some(19));
+        assert_eq!(dt.minute, Some(39));
+        assert_eq!(dt.second, Some(15));
+        assert_eq!(dt.tz, Some(TimeZone::UTC));
+    }
+}
+