diff --git a/Strings/LowercaseToUppercase.js b/Strings/LowercaseToUppercase.js
new file mode 100644
index 0000000..c9bdd76
--- /dev/null
+++ b/Strings/LowercaseToUppercase.js
@@ -0,0 +1,26 @@
+// upper converts lowercase sting to upper case
+// input is 1 string i.e. str
+const upper = (str) => {
+  // check that inputs are string
+  if (typeof str !== "string") {
+    return "Not string(s)";
+  }
+
+  var convertedString = "";
+
+  for (let i = 0; i < str.length; i++) {
+    if (str.charCodeAt(i) >= 97 && str.charCodeAt(i) <= 122) {
+      convertedString =
+        convertedString + String.fromCharCode(65 + str.charCodeAt(i) - 97);
+      continue;
+    }
+    convertedString = convertedString + str.charAt(i);
+  }
+
+  return convertedString;
+};
+
+console.log(upper("abcd")); // should print ABCD
+console.log(upper("abcd1")); // should print ABCD1
+console.log(upper("*abcd")); // *ABCD
+console.log(upper("aBs")); // should print ABS