diff --git a/src/components/Post/Post.tsx b/src/components/Post/Post.tsx
index a2def8d..2f1015b 100644
--- a/src/components/Post/Post.tsx
+++ b/src/components/Post/Post.tsx
@@ -29,7 +29,7 @@ export default function Post({
   closed,
 }: PostProps) {
   const timeRange = formatTimeRange(startsAt, workhour);
-  const isPast = isPastDate(startsAt, workhour);
+  const isPast = isPastDate(startsAt);
   const isDimmed = closed || isPast;
   const { displayRate, rateText } = getPayRateText(
     hourlyPay,
@@ -40,58 +40,58 @@ export default function Post({
     <Link to={link} className="no-underline text-inherit block">
       <article
         className={cn(
-          "relative flex w-full flex-col rounded-xl border border-gray-20 bg-white p-3 shadow-md transition hover:shadow-lg md:p-4",
+          "relative flex w-full flex-col rounded-xl border border-gray-20 bg-white p-3 shadow-md transition hover:shadow-lg sm:p-4",
         )}
       >
         <div className="relative">
           <img
             src={imageUrl}
             alt={name}
-            className="w-full h-[84px] overflow-hidden rounded-xl object-cover md:h-40"
+            className="w-full h-[84px] overflow-hidden rounded-xl object-cover sm:h-40"
             onError={(e) => {
               e.currentTarget.onerror = null;
               e.currentTarget.src = "/default-image.png";
             }}
           />
           {isDimmed && (
-            <h3 className="absolute inset-0 flex items-center justify-center rounded-md bg-black/70 text-sm text-gray-30 md:text-[28px]">
+            <h3 className="absolute inset-0 flex items-center justify-center rounded-md bg-black/70 text-sm text-gray-30 sm:text-[28px]">
               {closed ? "마감 완료" : "지난 공고"}
             </h3>
           )}
         </div>
 
         <div className={cn(isDimmed && "opacity-20")}>
-          <div className="mt-3 flex flex-col gap-2 md:mt-5">
-            <h3 className="text-base md:text-xl">{name}</h3>
-            <p className="flex items-start gap-[6px] text-xs font-normal text-gray-50 md:text-[14px] md:leading-[22px]">
-              <Time className="h-4 w-4 md:h-5 md:w-5" />
+          <div className="mt-3 flex flex-col gap-2 sm:mt-5">
+            <h3 className="text-base sm:text-xl">{name}</h3>
+            <p className="flex items-start gap-[6px] text-xs font-normal text-gray-50 sm:text-[14px] sm:leading-[22px]">
+              <Time className="h-4 w-4 sm:h-5 sm:w-5" />
               {timeRange}
             </p>
-            <p className="flex items-start gap-[6px] text-xs font-normal text-gray-50 md:text-[14px] md:leading-[22px]">
-              <Location className="h-4 w-4 md:h-5 md:w-5" />
+            <p className="flex items-start gap-[6px] text-xs font-normal text-gray-50 sm:text-[14px] sm:leading-[22px]">
+              <Location className="h-4 w-4 sm:h-5 sm:w-5" />
               {address1}
             </p>
           </div>
 
-          <div className="mt-4 flex flex-col items-start md:flex-row md:items-center md:justify-between">
-            <h2 className="text-lg md:text-2xl">
+          <div className="mt-4 flex flex-col items-start sm:flex-row sm:items-center sm:justify-between">
+            <h2 className="text-lg sm:text-2xl">
               {hourlyPay.toLocaleString()}원
             </h2>
 
             <span
               className={cn(
-                "mt-[5px] flex items-center gap-[2px] text-xs font-normal text-red-40 md:text-sm md:text-white md:px-3 md:py-2 md:rounded-[20px]",
+                "mt-[5px] flex items-center gap-[2px] text-xs font-normal text-red-40 sm:text-sm sm:text-white sm:px-3 sm:py-2 sm:rounded-[20px]",
                 displayRate >= 50
-                  ? "md:bg-red-40"
+                  ? "sm:bg-red-40"
                   : displayRate >= 25
-                    ? "md:bg-red-30"
-                    : "md:bg-red-20",
+                    ? "sm:bg-red-30"
+                    : "sm:bg-red-20",
                 displayRate > 0 ? "" : "opacity-0",
               )}
             >
               {rateText}
-              <ArrowUp className="hidden h-5 w-5 md:block" />
-              <ArrowUpBold className="h-4 w-4 md:hidden" />
+              <ArrowUp className="hidden h-5 w-5 sm:block" />
+              <ArrowUpBold className="h-4 w-4 sm:hidden" />
             </span>
           </div>
         </div>
diff --git a/src/utils/datetime.ts b/src/utils/datetime.ts
index 6b11d76..ad2b97b 100644
--- a/src/utils/datetime.ts
+++ b/src/utils/datetime.ts
@@ -50,10 +50,11 @@ export function formatTimeRange(startsAt: string, workhour: number): string {
  * @param startsAt - ISO 8601 형식의 날짜 문자열
  * @param workhour - 근무 시간 (시간 단위)
  */
-export function isPastDate(startsAt: string, workhour: number): boolean {
-  const start = new Date(startsAt);
-  const end = new Date(start.getTime() + workhour * ONE_HOUR_MS);
-  return end.getTime() < Date.now();
+export function isPastDate(startsAt: string): boolean {
+  const startMs = Date.parse(startsAt);
+  const nowMs = Date.now();
+
+  return startMs < nowMs;
 }
 
 export const getRelativeTimeFromNow = (input: string | Date): string => {