diff --git a/examples/percentage.ts b/examples/percentage.ts
new file mode 100644
index 0000000..2246ff6
--- /dev/null
+++ b/examples/percentage.ts
@@ -0,0 +1,3 @@
+import { percentage } from "../src/index";
+
+console.log(percentage(10, 100)); // 10
\ No newline at end of file
diff --git a/examples/randomstring.ts b/examples/randomstring.ts
index cbba693..7c500ae 100644
--- a/examples/randomstring.ts
+++ b/examples/randomstring.ts
@@ -1,4 +1,4 @@
-import { randomString } from "../src/index.ts";
+import { randomString } from "../src/index";
 
 console.log(randomString(10));
 // => (random 10-character string)
\ No newline at end of file
diff --git a/src/index.ts b/src/index.ts
index e5d6766..485bcbe 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1 +1,2 @@
-export { randomString } from './utils/randomstring.ts';
\ No newline at end of file
+export { randomString } from './utils/randomstring';
+export { percentage } from './utils/percentage';
\ No newline at end of file
diff --git a/src/utils/percentage.ts b/src/utils/percentage.ts
new file mode 100644
index 0000000..d0a6d33
--- /dev/null
+++ b/src/utils/percentage.ts
@@ -0,0 +1,12 @@
+export function percentage(partial: number, total: number, allowNumNot100 = false) {
+  if (total === 0) {
+    throw new Error('Total cannot be 0');
+  }
+  if (partial < 0 || total < 0) {
+    throw new Error('Partial and total must be non-negative');
+  }
+  if (!allowNumNot100 && partial > total) {
+    return 100;
+  }
+  return (partial / total) * 100;
+}
\ No newline at end of file
diff --git a/tests/percentage.test.ts b/tests/percentage.test.ts
new file mode 100644
index 0000000..376274f
--- /dev/null
+++ b/tests/percentage.test.ts
@@ -0,0 +1,30 @@
+// did I overenginner these tests?
+import { percentage } from "../src/index";
+import { describe, it, expect } from 'vitest';
+
+describe('percentage', () => {
+    it('should return 50% when 1 is half of 2', () => {
+        expect(percentage(1, 2)).toBe(50);
+    });
+    it('should return 0% when 0 is half of 2', () => {
+        expect(percentage(0, 2)).toBe(0);
+    });
+    it('should return 100% when 2 is half of 2', () => {
+        expect(percentage(2, 2)).toBe(100);
+    });
+    it('should return 100% when 2 is half of 1', () => {
+        expect(percentage(2, 1)).toBe(100);
+    });
+    it('should return 200% when 2 is half of 1 and allowNumNot100 is true', () => {
+        expect(percentage(2, 1, true)).toBe(200);
+    })
+    it('should throw an error when total is 0', () => {
+        expect(() => percentage(1, 0)).toThrow();
+    });
+    it('should throw an error when partial is negative', () => {
+        expect(() => percentage(-1, 2)).toThrow();
+    });
+    it('should throw an error when total is negative', () => {
+        expect(() => percentage(1, -2)).toThrow();
+    });
+})
\ No newline at end of file
diff --git a/tests/randomString.test.ts b/tests/randomString.test.ts
index 923bfd9..e29bea9 100644
--- a/tests/randomString.test.ts
+++ b/tests/randomString.test.ts
@@ -1,4 +1,4 @@
-import { randomString } from '../src/index.ts'
+import { randomString } from '../src/index'
 import { describe, it, expect } from 'vitest'
 
 describe('randomString', () => {
diff --git a/tsconfig.json b/tsconfig.json
index e2f56d7..3691b84 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -35,7 +35,7 @@
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
     // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
     // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
-    "allowImportingTsExtensions": true,               /* Allow imports to include TypeScript file extensions. Requires '--moduleResolution bundler' and either '--noEmit' or '--emitDeclarationOnly' to be set. */
+    "allowImportingTsExtensions": false,               /* Allow imports to include TypeScript file extensions. Requires '--moduleResolution bundler' and either '--noEmit' or '--emitDeclarationOnly' to be set. */
     // "resolvePackageJsonExports": true,                /* Use the package.json 'exports' field when resolving package imports. */
     // "resolvePackageJsonImports": true,                /* Use the package.json 'imports' field when resolving imports. */
     // "customConditions": [],                           /* Conditions to set in addition to the resolver-specific defaults when resolving imports. */