diff --git a/admin-spa/src/routes/Orders/partials/OrderForm.tsx b/admin-spa/src/routes/Orders/partials/OrderForm.tsx
index f6fd754..fd84203 100644
--- a/admin-spa/src/routes/Orders/partials/OrderForm.tsx
+++ b/admin-spa/src/routes/Orders/partials/OrderForm.tsx
@@ -185,26 +185,43 @@ export default function OrderForm({
     enabled: items.length > 0,
   });
 
+  // Get effective shipping address (use billing if not shipping to different address)
+  const effectiveShippingAddress = React.useMemo(() => {
+    if (shipDiff) {
+      return shippingData;
+    }
+    // Use billing address
+    return {
+      country: bCountry,
+      state: bState,
+      city: bCity,
+      postcode: bPost,
+      address_1: bAddr1,
+      address_2: '',
+    };
+  }, [shipDiff, shippingData, bCountry, bState, bCity, bPost, bAddr1]);
+
   // Check if shipping address is complete enough to calculate rates
   const isShippingAddressComplete = React.useMemo(() => {
+    const addr = effectiveShippingAddress;
     // Need at minimum: country, state (if applicable), city
-    if (!shippingData.country) return false;
-    if (!shippingData.city) return false;
+    if (!addr.country) return false;
+    if (!addr.city) return false;
     // If country has states, require state
-    const countryStates = states[shippingData.country];
-    if (countryStates && Object.keys(countryStates).length > 0 && !shippingData.state) {
+    const countryStates = states[addr.country];
+    if (countryStates && Object.keys(countryStates).length > 0 && !addr.state) {
       return false;
     }
     return true;
-  }, [shippingData.country, shippingData.state, shippingData.city, states]);
+  }, [effectiveShippingAddress, states]);
 
   // Calculate shipping rates dynamically
   const { data: shippingRates, isLoading: shippingLoading } = useQuery({
-    queryKey: ['shipping-rates', items.map(i => ({ product_id: i.product_id, qty: i.qty })), shippingData.country, shippingData.state, shippingData.city, shippingData.postcode, shippingData.address_1],
+    queryKey: ['shipping-rates', items.map(i => ({ product_id: i.product_id, qty: i.qty })), effectiveShippingAddress.country, effectiveShippingAddress.state, effectiveShippingAddress.city, effectiveShippingAddress.postcode, effectiveShippingAddress.address_1],
     queryFn: async () => {
       return api.post('/shipping/calculate', {
         items: items.map(i => ({ product_id: i.product_id, qty: i.qty })),
-        shipping: shippingData,
+        shipping: effectiveShippingAddress,
       });
     },
     enabled: isShippingAddressComplete && items.length > 0,
diff --git a/includes/Api/OrdersController.php b/includes/Api/OrdersController.php
index 01e7731..cae3c0a 100644
--- a/includes/Api/OrdersController.php
+++ b/includes/Api/OrdersController.php
@@ -1293,12 +1293,25 @@ class OrdersController {
 
       // Set customer shipping address
       if ( ! empty( $shipping ) ) {
-        WC()->customer->set_shipping_country( $shipping['country'] ?? '' );
-        WC()->customer->set_shipping_state( $shipping['state'] ?? '' );
-        WC()->customer->set_shipping_postcode( $shipping['postcode'] ?? '' );
-        WC()->customer->set_shipping_city( $shipping['city'] ?? '' );
-        WC()->customer->set_shipping_address( $shipping['address_1'] ?? '' );
-        WC()->customer->set_shipping_address_2( $shipping['address_2'] ?? '' );
+        $country = $shipping['country'] ?? '';
+        $state = $shipping['state'] ?? '';
+        $postcode = $shipping['postcode'] ?? '';
+        $city = $shipping['city'] ?? '';
+        $address_1 = $shipping['address_1'] ?? '';
+        $address_2 = $shipping['address_2'] ?? '';
+        
+        WC()->customer->set_shipping_country( $country );
+        WC()->customer->set_shipping_state( $state );
+        WC()->customer->set_shipping_postcode( $postcode );
+        WC()->customer->set_shipping_city( $city );
+        WC()->customer->set_shipping_address( $address_1 );
+        WC()->customer->set_shipping_address_2( $address_2 );
+        
+        // Also set billing for tax calculation context
+        WC()->customer->set_billing_country( $country );
+        WC()->customer->set_billing_state( $state );
+        WC()->customer->set_billing_postcode( $postcode );
+        WC()->customer->set_billing_city( $city );
       }
 
       // Calculate shipping