diff --git a/frontend/src/components/PriceChart.tsx b/frontend/src/components/PriceChart.tsx
index 1168e40..f0a7ea8 100644
--- a/frontend/src/components/PriceChart.tsx
+++ b/frontend/src/components/PriceChart.tsx
@@ -41,13 +41,15 @@ export default function PriceChart({
 
   const chartData = prices.map((p) => ({
     date: new Date(p.recorded_at).getTime(),
-    price: parseFloat(p.price.toString()),
+    price: typeof p.price === 'string' ? parseFloat(p.price) : p.price,
   }));
 
-  const minPrice = Math.min(...chartData.map((d) => d.price));
-  const maxPrice = Math.max(...chartData.map((d) => d.price));
-  const avgPrice =
-    chartData.reduce((sum, d) => sum + d.price, 0) / chartData.length;
+  const priceValues = chartData.map((d) => d.price).filter((p) => !isNaN(p));
+  const minPrice = priceValues.length > 0 ? Math.min(...priceValues) : 0;
+  const maxPrice = priceValues.length > 0 ? Math.max(...priceValues) : 0;
+  const avgPrice = priceValues.length > 0
+    ? priceValues.reduce((sum, p) => sum + p, 0) / priceValues.length
+    : 0;
 
   const formatDate = (timestamp: number) => {
     const date = new Date(timestamp);
@@ -55,6 +57,7 @@ export default function PriceChart({
   };
 
   const formatPrice = (value: number) => {
+    if (value === null || value === undefined || isNaN(value)) return 'N/A';
     return `${currencySymbol}${value.toFixed(2)}`;
   };
 
diff --git a/frontend/src/components/ProductCard.tsx b/frontend/src/components/ProductCard.tsx
index 9253fc4..6dd7bf5 100644
--- a/frontend/src/components/ProductCard.tsx
+++ b/frontend/src/components/ProductCard.tsx
@@ -7,11 +7,13 @@ interface ProductCardProps {
 }
 
 export default function ProductCard({ product, onDelete }: ProductCardProps) {
-  const formatPrice = (price: number | null, currency: string | null) => {
-    if (price === null) return 'N/A';
+  const formatPrice = (price: number | string | null, currency: string | null) => {
+    if (price === null || price === undefined) return 'N/A';
+    const numPrice = typeof price === 'string' ? parseFloat(price) : price;
+    if (isNaN(numPrice)) return 'N/A';
     const currencySymbol =
       currency === 'EUR' ? '€' : currency === 'GBP' ? '£' : '$';
-    return `${currencySymbol}${price.toFixed(2)}`;
+    return `${currencySymbol}${numPrice.toFixed(2)}`;
   };
 
   const formatDate = (dateStr: string | null) => {
diff --git a/frontend/src/pages/ProductDetail.tsx b/frontend/src/pages/ProductDetail.tsx
index 11db18b..6cab046 100644
--- a/frontend/src/pages/ProductDetail.tsx
+++ b/frontend/src/pages/ProductDetail.tsx
@@ -71,11 +71,13 @@ export default function ProductDetail() {
     fetchData(days);
   };
 
-  const formatPrice = (price: number | null, currency: string | null) => {
-    if (price === null) return 'N/A';
+  const formatPrice = (price: number | string | null, currency: string | null) => {
+    if (price === null || price === undefined) return 'N/A';
+    const numPrice = typeof price === 'string' ? parseFloat(price) : price;
+    if (isNaN(numPrice)) return 'N/A';
     const currencySymbol =
       currency === 'EUR' ? '€' : currency === 'GBP' ? '£' : '$';
-    return `${currencySymbol}${price.toFixed(2)}`;
+    return `${currencySymbol}${numPrice.toFixed(2)}`;
   };
 
   if (isLoading) {
@@ -105,10 +107,17 @@ export default function ProductDetail() {
     );
   }
 
-  const priceChange =
-    product.stats && prices.length > 1
-      ? ((product.current_price || 0) - prices[0].price) / prices[0].price
-      : null;
+  const priceChange = (() => {
+    if (!product.stats || prices.length < 1) return null;
+    const currentPrice = typeof product.current_price === 'string'
+      ? parseFloat(product.current_price)
+      : (product.current_price || 0);
+    const firstPrice = typeof prices[0].price === 'string'
+      ? parseFloat(prices[0].price)
+      : prices[0].price;
+    if (firstPrice === 0) return null;
+    return (currentPrice - firstPrice) / firstPrice;
+  })();
 
   return (
     <Layout>