diff --git a/2023/day04/main.go b/2023/day04/main.go
new file mode 100644
index 0000000..3e1400c
--- /dev/null
+++ b/2023/day04/main.go
@@ -0,0 +1,138 @@
+package main
+
+import (
+	_ "embed"
+	"flag"
+	"fmt"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/cast"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+//go:embed input.txt
+var input string
+
+func init() {
+	// do this in init (not main) so test file has same input
+	input = strings.TrimRight(input, "\n")
+	if len(input) == 0 {
+		panic("empty input.txt file")
+	}
+}
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	if part == 1 {
+		ans := part1(input)
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
+		fmt.Println("Output:", ans)
+	} else {
+		ans := part2(input)
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
+		fmt.Println("Output:", ans)
+	}
+}
+
+func part1(input string) int {
+	parsed := parseInput(input)
+
+	var ans int
+
+	for _, card := range parsed {
+		ans += scoreCard(card)
+	}
+
+	return ans
+}
+
+func scoreCard(c card) int {
+	var ans int
+
+	for _, num := range c.hand {
+		if c.winning[num] {
+			if ans == 0 {
+				ans = 1
+			} else {
+				ans *= 2
+			}
+		}
+	}
+
+	return ans
+}
+
+func part2(input string) int {
+	cards := parseInput(input)
+
+	// tracks the number of cards won, starts with 1 of each card
+	numCards := make([]int, len(cards))
+	for i := range numCards {
+		numCards[i] = 1
+	}
+
+	for index, c := range cards {
+		cardsWon := countWinningNumbers(c)
+		for i := 1; i <= cardsWon; i++ {
+			// add number of current card to account for previous wins
+			numCards[index+i] += numCards[index]
+		}
+	}
+
+	// add up total number of cards
+	var cardCount int
+	for _, n := range numCards {
+		cardCount += n
+	}
+	return cardCount
+}
+
+func countWinningNumbers(c card) int {
+	var ans int
+
+	for _, num := range c.hand {
+		if c.winning[num] {
+			ans++
+		}
+	}
+
+	return ans
+}
+
+type card struct {
+	// index   int // unused
+	winning map[int]bool
+	hand    []int
+}
+
+func parseInput(input string) (ans []card) {
+	for _, line := range strings.Split(input, "\n") {
+		c := card{
+			// index:   len(ans) + 1,
+			winning: map[int]bool{},
+		}
+
+		half := strings.Split(line, ": ")
+		numParts := strings.Split(half[1], " | ")
+		for _, winningNum := range strings.Split(numParts[0], " ") {
+			// handles single digits that have an extra empty string between nums
+			if winningNum == "" {
+				continue
+			}
+			c.winning[cast.ToInt(winningNum)] = true
+		}
+
+		for _, handNum := range strings.Split(numParts[1], " ") {
+			if handNum == "" {
+				continue
+			}
+			c.hand = append(c.hand, cast.ToInt(handNum))
+		}
+		ans = append(ans, c)
+	}
+	return ans
+}
diff --git a/2023/day04/main_test.go b/2023/day04/main_test.go
new file mode 100644
index 0000000..053e861
--- /dev/null
+++ b/2023/day04/main_test.go
@@ -0,0 +1,64 @@
+package main
+
+import (
+	"testing"
+)
+
+var example = `Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53
+Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
+Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1
+Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83
+Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
+Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11`
+
+func Test_part1(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  int
+	}{
+		{
+			name:  "example",
+			input: example,
+			want:  13,
+		},
+		{
+			name:  "actual",
+			input: input,
+			want:  19135,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part1(tt.input); got != tt.want {
+				t.Errorf("part1() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func Test_part2(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  int
+	}{
+		{
+			name:  "example",
+			input: example,
+			want:  30,
+		},
+		{
+			name:  "actual",
+			input: input,
+			want:  5704953,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part2(tt.input); got != tt.want {
+				t.Errorf("part2() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}