diff --git a/app/usage.js b/app/usage.js
index 5c24bba..16778a0 100644
--- a/app/usage.js
+++ b/app/usage.js
@@ -211,23 +211,32 @@ function round1(n) {
 
 const RATE_KIND_LABEL = { tokens: 'token', requests: '次數' };
 
+/** 是否為有限正數（排除 0、負數、NaN、Infinity），避免算出 Infinity%／NaN%／負百分比。 */
+function isFinitePositive(n) {
+  return Number.isFinite(Number(n)) && Number(n) > 0;
+}
+
 /**
  * 計算「剩餘可用百分比」，依優先序擇一：
- * 1. 帳號額度（quota 有上限）→ 剩餘 credits / 上限；
- * 2. 速率配額（rate limit header）→ 當前視窗剩餘 / 上限；
- * 皆無法取得時回傳 { percent: null, reason }。
+ * 1. 帳號額度（quota 有有限正數上限）→ 剩餘 credits / 上限；
+ * 2. 速率配額（rate limit header，有限正數上限）→ 當前視窗剩餘 / 上限；
+ * 上限或剩餘為 0／負數／NaN／Infinity 等無效值時不計算，落到 { percent: null, reason }。
  */
 export function resolveRemainingPercent(quota, rate) {
-  if (quota?.available && quota.limit != null && Number(quota.limit) > 0) {
+  if (quota?.available && quota.limit != null && isFinitePositive(quota.limit)) {
     const limit = Number(quota.limit);
     const remaining = quota.remaining == null ? limit - num(quota.used) : Number(quota.remaining);
-    return { percent: round1((remaining / limit) * 100), basis: '帳號額度', remaining, limit, unit: quota.currency || '' };
+    if (Number.isFinite(remaining)) {
+      return { percent: round1((remaining / limit) * 100), basis: '帳號額度', remaining, limit, unit: quota.currency || '' };
+    }
   }
-  if (rate?.hasData && Number(rate.limit) > 0) {
+  if (rate?.hasData && isFinitePositive(rate.limit)) {
     const limit = Number(rate.limit);
     const remaining = Number(rate.remaining);
-    const kindLabel = RATE_KIND_LABEL[rate.kind] || rate.kind;
-    return { percent: round1((remaining / limit) * 100), basis: `速率配額（當前視窗，${kindLabel}）`, remaining, limit, unit: '' };
+    if (Number.isFinite(remaining)) {
+      const kindLabel = RATE_KIND_LABEL[rate.kind] || rate.kind;
+      return { percent: round1((remaining / limit) * 100), basis: `速率配額（當前視窗，${kindLabel}）`, remaining, limit, unit: '' };
+    }
   }
   let reason;
   if (quota?.available && quota.limit == null) reason = '帳號額度無上限，無法計算百分比';