diff --git a/app/favicon.ico b/app/favicon.ico
index 718d6fe..73ef88d 100644
Binary files a/app/favicon.ico and b/app/favicon.ico differ
diff --git a/app/page.tsx b/app/page.tsx
index d7a8f68..40b1583 100644
--- a/app/page.tsx
+++ b/app/page.tsx
@@ -11,8 +11,6 @@ export default async function Home() {
 	const session = await auth();
 	if (!session?.user) return null;
 
-	console.log(session);
-
 	return (
 		<div className="grid grid-cols-1 md:grid-cols-3 gap-8 h-full pt-24 px-4 text-accent-foreground md:items-center justify-items-center">
 			<div className="col-span-1 w-full max-w-md space-y-8 text-center">
@@ -49,6 +47,7 @@ export default async function Home() {
 							width={20}
 							height={20}
 							className="dark:hidden"
+							priority
 						/>
 						<Image
 							src={GitHubBlack}
@@ -56,6 +55,7 @@ export default async function Home() {
 							width={20}
 							height={20}
 							className="hidden dark:block"
+							priority
 						/>
 						振り返りを見る
 					</Link>
@@ -69,6 +69,7 @@ export default async function Home() {
 					width={700}
 					height={800}
 					className="w-full h-auto mx-auto rounded-md"
+					priority
 				/>
 			</div>
 		</div>
diff --git a/app/recap/components/calculate-change-rate.ts b/app/recap/components/calculate-change-rate.ts
new file mode 100644
index 0000000..8abd8a0
--- /dev/null
+++ b/app/recap/components/calculate-change-rate.ts
@@ -0,0 +1,28 @@
+/**
+ * 去年の数値(prevYear) と 今年の数値(currentYear)を引数に取り、
+ * 数値(小数第2位まで) か "-" を返す関数
+ *
+ * @param {number} prevYear - 去年のコミット数や指標となる数値
+ * @param {number} currentYear - 今年のコミット数や指標となる数値
+ * @returns {number|"-"} - 有効な場合は数値型、無効の場合は "-"
+ */
+export function calculateChangeRate(
+	prevYear: number,
+	currentYear: number,
+): number | "-" {
+	if (typeof prevYear !== "number" || typeof currentYear !== "number") {
+		return "-";
+	}
+
+	if (prevYear === 0) {
+		return "-";
+	}
+
+	const ratio = ((currentYear - prevYear) / prevYear) * 100;
+
+	if (!Number.isFinite(ratio)) {
+		return "-";
+	}
+
+	return Number.parseFloat(ratio.toFixed(2));
+}
diff --git a/app/recap/components/overview.tsx b/app/recap/components/overview.tsx
index 6d8cc70..03f48e4 100644
--- a/app/recap/components/overview.tsx
+++ b/app/recap/components/overview.tsx
@@ -18,6 +18,7 @@ import {
 	UsersRound,
 } from "lucide-react";
 import type { FC } from "react";
+import { calculateChangeRate } from "./calculate-change-rate";
 import { LanguagesUsageGraph } from "./graph/languages";
 import { MonthlyContributionsGraph } from "./graph/monthly";
 import { WeeklyContributionsGraph } from "./graph/weekly";
@@ -98,12 +99,10 @@ export const OverView: FC<Props> = async ({ data }) => {
 							<p className="text-xs text-muted-foreground">
 								前年と比較して
 								<b>
-									{(
-										((data.totalCommitCount -
-											data.previousYearStats.totalCommitCount) /
-											data.previousYearStats.totalCommitCount) *
-										100
-									).toFixed(2)}
+									{calculateChangeRate(
+										data.previousYearStats.totalCommitCount,
+										data.totalCommitCount,
+									)}
 								</b>
 								% 増加しました。
 							</p>
@@ -123,12 +122,10 @@ export const OverView: FC<Props> = async ({ data }) => {
 							<p className="text-xs text-muted-foreground">
 								前年と比較して
 								<b>
-									{(
-										((data.closedIssuesAssigned -
-											data.previousYearStats.closedIssuesAssignedCount) /
-											data.previousYearStats.closedIssuesAssignedCount) *
-										100
-									).toFixed(2)}
+									{calculateChangeRate(
+										data.previousYearStats.closedIssuesAssignedCount,
+										data.closedIssuesAssigned,
+									)}
 								</b>
 								% 増加しました。
 							</p>
@@ -148,12 +145,10 @@ export const OverView: FC<Props> = async ({ data }) => {
 							<p className="text-xs text-muted-foreground">
 								前年と比較して
 								<b>
-									{(
-										((data.openedPullRequests -
-											data.previousYearStats.openedPullRequests) /
-											data.previousYearStats.openedPullRequests) *
-										100
-									).toFixed(2)}
+									{calculateChangeRate(
+										data.previousYearStats.openedPullRequests,
+										data.openedPullRequests,
+									)}
 								</b>
 								% 増加しました。
 							</p>
@@ -173,12 +168,10 @@ export const OverView: FC<Props> = async ({ data }) => {
 							<p className="text-xs text-muted-foreground">
 								前年と比較して
 								<b>
-									{(
-										((data.reviewedPullRequests -
-											data.previousYearStats.reviewedPullRequests) /
-											data.previousYearStats.reviewedPullRequests) *
-										100
-									).toFixed(2)}
+									{calculateChangeRate(
+										data.previousYearStats.reviewedPullRequests,
+										data.reviewedPullRequests,
+									)}
 								</b>
 								% 増加しました。
 							</p>
diff --git a/lib/auth.ts b/lib/auth.ts
index 8e76153..305d4c8 100644
--- a/lib/auth.ts
+++ b/lib/auth.ts
@@ -7,7 +7,7 @@ export const { handlers, auth, signIn, signOut } = NextAuth({
 		GitHub({
 			authorization: {
 				param: {
-					scope: "repo read:user",
+					scope: "repo",
 				},
 			},
 		}),