Working in cross-border payments, banking, and licensing, I need to see where people are geographically, what time it is for them, and what a proposed meeting time means for me in Istanbul. That is why I built Meridian Clock, a free world clock and time zone converter for Chrome.

If someone says, “We’ll speak at 3 PM Montevideo time,” I want to enter that date and time and immediately see what it means in Istanbul and for everyone else on the call. I want the geography and the clocks in one place.

Walk into any old-school FX dealing room and you will see the classic fix: a row of clocks on the wall, each one labelled with a city. New York, London, Tokyo. It looks impressive. Truth be told, it only answers one question: what time is it there right now?

The question I actually need answered is a different one. If my partner in New York says “Tuesday, 5:30 PM,” what is that for me, and for everyone else on the call?

Isn’t it just adding and subtracting hours?

No. And this is where time zone conversion gets interesting.

Let’s say someone in New York suggests 1:30 AM on 1 November 2026. Odd hour, I know, but stay with me. That morning the clocks in New York go back from 2:00 AM to 1:00 AM. So 1:30 AM happens twice: once at UTC−4, and once again an hour later at UTC−5. Two different moments, same time on the wall.

A converter that silently picks one has made a decision you may not even know about.

Now flip it. On 8 March 2026, New York’s clocks jump from 2:00 AM straight to 3:00 AM. So 2:30 AM that day does not exist. A tool that quietly shifts it to another time might give you an answer, but it has changed the question. Those are the 2026 daylight-saving transition dates confirmed by NIST.

Then there is Kathmandu, which runs 5 hours and 45 minutes ahead of UTC. Not 5, not 6. Quarter-hour offsets are real. You can see Nepal’s UTC+5:45 rule in the IANA time zone data for Asia.

Time zones are not math. They are politics.

Countries change their clock rules, sometimes with very little notice. Any tool that “just adds hours” without knowing the rules for the date is betting that no government ever changes its mind.

So I built Meridian Clock

Meridian Clock is a free extension for Google Chrome. It opens in its own tab and shows the world on a live map, with the day and night sides shaded as the sun moves. Along the bottom is a ruler of up to ten of your cities, each with its local time, date, and how far ahead or behind it is from your home city.

Click any city, type a date and time in that city, and apply it. Everything else converts to that moment. If you want Montevideo on your ruler, use Add city to find it and save it.

When you hit a 1:30 AM that happens twice, it asks you which one you mean. When you hit a 2:30 AM that doesn’t exist, it tells you the clocks jump from 2:00 to 3:00 and asks you for a real time.

It doesn’t silently guess which occurrence you intended or move you past a skipped hour.

The time zone rules come from the IANA Time Zone Database, the widely used record of local clock rules and their changes. Meridian Clock uses the time zone data available through Chrome rather than fetching it from a server. Keeping Chrome updated matters, especially when a country changes its rules.

The city ruler is ordered by each city’s UTC offset at the time you are viewing, so its order can change with daylight saving. The sunrise, sunset, and day/night shading are estimates; the legal clock times follow the time zone rules.

Your data stays on your computer

In payments we preach data minimisation, which means collecting only what you absolutely need. Then we install tools that collect everything.

Meridian Clock has no account, no tracking, and no ads. Once installed, it works entirely offline. Its maps, city data, and fonts are bundled with it. It doesn’t even ask to read your tabs.

The only permission it requests is storage, to save your settings on your own machine: your cities, home city, map labels, 12- or 24-hour time, and dark or light theme. The privacy policy explains exactly what is stored.

That’s it.

Free, and open for anyone to check

The code is open source under the MIT licence. In plain English, anyone can read it, use it, change it, or build on it, for free, while keeping the required copyright and licence notice. If you don’t trust my word about privacy, you don’t have to. The code is right there.

It is the sort of practical, personal tool I had in mind when I wrote about coding at the speed of thought: a specific frustration, turned into software I can actually use.

How to install Meridian Clock in Chrome

Installation is through GitHub. You will need Chrome 120 or later.

1. Open the latest Meridian Clock release and download the meridian-clock-<version>.zip attachment, rather than GitHub’s automatically generated “Source code” ZIP.
2. Unzip it into a permanent folder. Chrome will keep loading the extension from that location, so leave the folder there.
3. Open chrome://extensions in Chrome and turn on Developer mode in the top-right corner.
4. Click Load unpacked and select the meridian-clock folder that contains manifest.json.
5. Pin Meridian Clock using the puzzle-piece menu in Chrome’s toolbar, then click its icon to open your world clock.

If you find a time zone it gets wrong, please tell me. Open an issue on GitHub. Edge cases are exactly what I want to hear about.

Interesting times we live in, in every time zone.