Comparing across timezones
Tuesday 3 PM in Seoul is Monday 2 AM in New York. Use it when scheduling video calls or planning a trip across timezones.
Change the base time and every row updates with it. Five cities (Seoul · UTC · New York · London · Tokyo) are preloaded; add or remove others via search.
How it works
The browser's Intl.DateTimeFormat API queries the IANA timezone database. No extra library to download — every city your operating system knows about is searchable. DST transitions (March / November) are applied automatically.
UTC offsets render as +9, -5, etc., with half-hour offsets (UTC+9:30) handled precisely. Short names (KST · EST · JST) are also shown, ready to paste into emails or calendar invites.
Use cases
Cross-border collaboration — Confirm a meeting time falls within both sides' working hours (typically 9 AM – 6 PM).
Travel itineraries — Track departure / layover / arrival times side by side to plan connections and hotel check-ins.
International emails — Write lines like "Tuesday 3 PM KST = Monday 11 PM PST" with both timezones explicit.
Data handling
The base time and your selected cities are stored only in sessionStorage and disappear when you close the tab. Nothing is uploaded.
Base time · cities never leave the page
Both the base time and your city list are stored only in sessionStorage and disappear when you close the tab. Timezone lookups go through the browser Intl API — zero external traffic.