diff --git a/index.ts b/index.ts
index 3bd2ad1..1994fcb 100644
--- a/index.ts
+++ b/index.ts
@@ -1,3 +1,3 @@
-import { runDayThree } from "./src/day_three";
+import {runDayFour} from "./src/day_four";
 
-runDayThree();
\ No newline at end of file
+runDayFour();
\ No newline at end of file
diff --git a/src/day_four.test.ts b/src/day_four.test.ts
new file mode 100644
index 0000000..71f7cce
--- /dev/null
+++ b/src/day_four.test.ts
@@ -0,0 +1,41 @@
+import {Scratchcard, ScratchcardSet} from "./day_four";
+
+describe('Day 4', () => {
+	const inputs: [string, number][] = [
+		['Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53', 8],
+		['Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19', 2],
+		['Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1', 2],
+		['Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83', 1],
+		['Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36', 0],
+		['Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11', 0]
+	];
+
+	it.each(inputs)('should score %s with %d', (input, expectedScore) => {
+		const scratchcard = new Scratchcard(input);
+		expect(scratchcard.score).toEqual(expectedScore);
+	});
+
+	it.each(inputs.map(([input, score]) => [input, score !== 0]))('should return whether %s is a winner', (input, winner) => {
+		const scratchcard = new Scratchcard(input);
+
+		expect(scratchcard.isWinner).toEqual(winner);
+	});
+
+	it('should report the correct scratchcard size', () => {
+		const scratchcard = new Scratchcard(inputs[0][0]);
+		const children = inputs.slice(1, 5).map(([input]) => new Scratchcard(input));
+
+		scratchcard.setChildren(children);
+		expect(scratchcard.size).toEqual(5);
+	});
+
+	it('should calculate the total score', () => {
+		const scratchcards = new ScratchcardSet(inputs.map(([input]) => input));
+		expect(scratchcards.totalScore).toEqual(13);
+	});
+
+	it('should calculate the total number of scratchcards', () => {
+		const scratchcards = new ScratchcardSet(inputs.map(([input]) => input));
+		expect(scratchcards.length).toEqual(30);
+	});
+});
\ No newline at end of file
diff --git a/src/day_four.ts b/src/day_four.ts
new file mode 100644
index 0000000..f819e03
--- /dev/null
+++ b/src/day_four.ts
@@ -0,0 +1,76 @@
+import fs from "fs";
+import {Engine} from "./day_three";
+import {forEach} from "lodash";
+
+export class Scratchcard {
+	private readonly numbers: number[];
+	private readonly winningNumbers: number[];
+	private children: Scratchcard[] = [];
+
+	constructor(input: string) {
+		const [_, withoutId] = input.split(':');
+		const [winning, ourNumbers] = withoutId.split('|');
+
+		this.winningNumbers = this.parseNumberList(winning);
+		this.numbers = this.parseNumberList(ourNumbers);
+	}
+
+	private parseNumberList(input: string): number[] {
+		return [...input.matchAll(/\d+/g)].map(match => parseInt(match[0], 10));
+	}
+
+	public get matches() {
+		return this.numbers.filter(number => this.winningNumbers.includes(number));
+	}
+
+	get score() {
+		const matches = this.matches;
+		if (!matches.length) return 0;
+		if (matches.length === 1) return 1;
+
+		return Math.pow(2, Math.max(matches.length - 1, 1));
+	}
+
+	get isWinner() {
+		return Boolean(this.matches.length);
+	}
+
+	public setChildren(children: Scratchcard[]) {
+		this.children = children;
+	}
+
+	get size(): number {
+		return 1 + this.children.reduce((totalSize, child) => totalSize + child.size, 0);
+	}
+}
+
+export class ScratchcardSet {
+	private readonly scratchcards: Scratchcard[];
+
+	constructor(inputs: string[]) {
+		this.scratchcards = inputs.map(input => new Scratchcard(input));
+
+		this.scratchcards.forEach((scratchcard, index) => {
+			if (scratchcard.isWinner) {
+				const children = this.scratchcards.slice(index + 1, index + 1 + scratchcard.matches.length);
+				scratchcard.setChildren(children);
+			}
+		});
+	}
+
+	get totalScore() {
+		return this.scratchcards.reduce((total, scratchcard) => total + scratchcard.score, 0);
+	}
+
+	get length() {
+		return this.scratchcards.reduce((totalSize, scratchcard) => totalSize + scratchcard.size, 0);
+	}
+}
+
+export const runDayFour = () => {
+	const input = fs.readFileSync('./inputs/day_four_input.txt', 'utf8').split('\n').filter(Boolean);
+	const scratchCards =  new ScratchcardSet(input);
+
+	console.log(scratchCards.totalScore);
+	console.log(scratchCards.length);
+}
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