diff --git a/src/day4.rs b/src/day4.rs
new file mode 100644
index 0000000..9329b27
--- /dev/null
+++ b/src/day4.rs
@@ -0,0 +1,67 @@
+use std::{io::BufRead, ops::RangeInclusive};
+
+use aoc_runner_derive::{aoc, aoc_generator};
+
+struct Pair([RangeInclusive<u64>; 2]);
+
+impl From<&str> for Pair {
+    fn from(value: &str) -> Self {
+        let ranges = value.split_once(',').unwrap();
+        Pair([parse_range(ranges.0), parse_range(ranges.1)])
+    }
+}
+
+impl Pair {
+    fn fully_contained(&self) -> bool {
+        (self.0[0].start() <= self.0[1].start() && self.0[0].end() >= self.0[1].end())
+            || (self.0[1].start() <= self.0[0].start() && self.0[1].end() >= self.0[0].end())
+    }
+    fn overlaps(&self) -> bool {
+        self.0[0].contains(self.0[1].start())
+            || self.0[0].contains(self.0[1].end())
+            || self.0[1].contains(self.0[0].start())
+            || self.0[1].contains(self.0[0].end())
+    }
+}
+
+fn parse_range(s: &str) -> RangeInclusive<u64> {
+    let (lower, upper) = s.split_once('-').unwrap();
+    RangeInclusive::new(lower.parse().unwrap(), upper.parse().unwrap())
+}
+
+#[aoc_generator(day4)]
+fn parse(input: &str) -> Vec<Pair> {
+    input.lines().map(|l| l.into()).collect()
+}
+
+#[aoc(day4, part1)]
+fn part1(input: &Vec<Pair>) -> u64 {
+    input.iter().filter(|p| p.fully_contained()).count() as u64
+}
+
+#[aoc(day4, part2)]
+fn part2(input: &Vec<Pair>) -> u64 {
+    input.iter().filter(|p| p.overlaps()).count() as u64
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const EXAMPLE: &str = "2-4,6-8
+2-3,4-5
+5-7,7-9
+2-8,3-7
+6-6,4-6
+2-6,4-8";
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(part1(&parse(EXAMPLE)), 2);
+    }
+
+    #[test]
+    fn part2_example() {
+        assert_eq!(part2(&parse(EXAMPLE)), 4);
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 72cdbc0..53776f7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,4 @@
+mod day4;
 mod day1;
 mod day2;
 mod day3;