diff --git a/Maths/decimal-to-octal.js b/Maths/decimal-to-octal.js
new file mode 100644
index 0000000..6c1bbd1
--- /dev/null
+++ b/Maths/decimal-to-octal.js
@@ -0,0 +1,15 @@
+function convertToOctal(num) {
+  if (typeof num !== "number") {
+    throw new Error("Input must be a valid number.");
+  }
+
+  if (num <= 0 || num >= 1e9) {
+    throw new Error(
+      "Number must be greater than zero and less than one billion."
+    );
+  }
+
+  return num.toString(8);
+}
+
+console.log(convertToOctal(63)); // 77