diff --git a/projects/tip-calculator/index.js b/projects/tip-calculator/index.js
index 98cb079..69fff45 100644
--- a/projects/tip-calculator/index.js
+++ b/projects/tip-calculator/index.js
@@ -4,10 +4,17 @@ const tipInput = document.getElementById("tip");
 const totalSpan = document.getElementById("total");
 
 function calculateTotal() {
-  const billValue = billInput.value;
-  const tipValue = tipInput.value;
+   const billValue = Number(billInput.value);
+  const tipValue = Number(tipInput.value);
   const totalValue = billValue * (1 + tipValue / 100);
   totalSpan.innerText = totalValue.toFixed(2);
 }
 
 btnEl.addEventListener("click", calculateTotal);
+
+billInput.addEventListener("input", () => {
+  if (billInput.value < 0) billInput.value = 0;
+});
+tipInput.addEventListener("input", () => {
+  if (tipInput.value < 0) tipInput.value = 0;
+});
\ No newline at end of file