Timezone Converter Pro

Convert a date & time across any IANA timezone and find a meeting slot everyone can make — fast, private, and fully offline.

A premium, zero-dependency timezone workbench. Pick a date, time and source zone, add as many comparison zones as you like, and instantly see accurate local times plus a horizontal working-hours timeline — all computed from the browser's own Intl API, with nothing ever leaving your machine.

Overview

Timezone Converter Pro is part of the Web Utility Suite. It runs entirely in the browser with no build step, no frameworks, no bundled timezone database, and no network calls — open index.html from disk and it works. It relies exclusively on Intl.DateTimeFormat and Intl.supportedValuesOf('timeZone'), so the timezone data (including DST rules) is always as current as the browser itself.

The core challenge this tool solves correctly: an <input type="datetime-local"> value is timezone-naive. To know what instant in time the user means, the wall-clock value has to be reinterpreted as belonging to the chosen source timezone — and that requires knowing that zone's UTC offset at that instant, which itself depends on DST. The app resolves this with a small converging iteration against Intl.DateTimeFormat.formatToParts, rather than a static offset table, so it stays correct through DST transitions in every zone the browser knows about.

Features

• Source picker — a date+time field plus a searchable timezone field (autocomplete over every IANA zone the browser supports), defaulting to your detected local timezone.
• Accurate wall-clock → UTC conversion — a DST-aware iterative algorithm (no hardcoded offsets) turns the entered local date/time + source zone into a precise UTC instant.
• Comparison zones — add or remove any number of target timezones as chips; your selection is remembered between visits.
• Results grid — every comparison zone's converted local time, date, zone abbreviation and UTC offset, recomputed live as you type.
• Copy summary — copy a plain-text summary of the source time and every conversion to the clipboard.
• Meeting planner timeline — a 24-hour horizontal strip per zone, aligned to the source zone's calendar day, highlighting each zone's configurable working hours so a shared green column reveals a good meeting window at a glance. A live "now" marker shows on the current day.
• Configurable working hours — set the start/end hour used to highlight the timeline (defaults to 09:00–17:00), including overnight ranges.
• Auto-persist — your source zone, comparison zones and working-hours preference are saved to localStorage and restored on return.
• Dark & light themes, fully responsive down to 360px (grid and timeline scroll independently, no page-wide horizontal scroll), and keyboard-driven.

Installation

No dependencies, no build step.

git clone https://github.com/kasapdev/timezone-converter-pro.git
cd timezone-converter-pro

Then simply open index.html in any modern browser (double-click it, or file:// it). That's it.

Usage

1. Set the Date & time and Source timezone — or click Now for the current moment, or My timezone to use your detected local zone.
2. Add comparison zones under Compare against by typing a zone name (autocomplete helps) and clicking Add, or pressing Enter in the field.
3. Read the Converted times grid — each card shows the local time, date, zone abbreviation and UTC offset for that zone at the chosen instant. Remove a zone from its card or its chip.
4. Click Copy summary to copy a plain-text breakdown of all conversions.
5. Scroll down to the Meeting planner — adjust Working hours if needed, then look for a column where every row is highlighted: that's a time that works for everyone.

Keyboard Shortcuts

Action	Shortcut
Jump to current date & time	N
Focus "Add timezone" field	Ctrl/⌘ + K
Use my local timezone as source	Ctrl/⌘ + L
Show shortcuts help	?
Close dialog	Esc

Screenshots

Screenshots coming soon.

Roadmap

• Shareable links that encode the source time and selected zones in the URL
• Drag-to-reorder comparison zones
• 12-hour / 24-hour display toggle
• Export the meeting planner grid as an image
• Recurring weekly meeting view across zones

License

MIT Licensed. Part of the Web Utility Suite.

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Part of the kasapdev Tools Suite

One of 45+ zero-dependency vanilla JS tools, all free and open source — see the full list.