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Time Difference Between Cities

The question is never really “what is the difference in hours”. It is “can I call now” and “what time will our three o’clock be for them”. Both are on this page: the clocks run by themselves, and a slider moves the moment you are asking about.

    The colour of a row is the local time of day: green for working hours, amber for early morning and evening, grey for night. The same thing is written in words next to the city — that is the answer to “can I call now”, without the arithmetic.

    Everything is counted in your browser: the time zone rules, including daylight saving, are already there. Nothing is uploaded, nothing is downloaded, and the page keeps working with the network off.

    Half-hour zones are shown as they are: India is 5:30 from London, Nepal 5:45. Rounding those to whole hours would be wrong for a billion and a half people — so the difference is written with minutes.

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    How to use

    1. Your own time zone is picked up from the browser and sits first, as the point of reference.
    2. Add the cities you care about — they are remembered for next time.
    3. Move the slider to the hour of your meeting: every city shows that same moment, with tomorrow and yesterday marked.

    Good to know

    Two questions, one screen

    “What time is it there” is about the current moment; the clocks answer it by themselves. “What time will our meeting be for them” is about a moment that has not happened yet, and without it the page is just a set of clocks. So the moment is a slider, set to now by default — and the same row of cities answers both questions without switching modes.

    Tomorrow and yesterday, not just hours

    In Tokyo it may already be tomorrow; in Honolulu, still yesterday. A difference of “−8 hours” reads wrongly in exactly the cases people look it up for, so every city shows its own date shift next to the clock. The shift is worked out from the calendar dates, not by dividing hours by 24: between Tokyo and Honolulu the gap is nineteen hours, and arithmetic gets that wrong.

    Nothing is downloaded, because the browser already knows

    Time zone rules — including daylight saving, which countries change by law more often than we ship builds — are already inside your browser. The page asks it rather than carrying a table that would go stale: no model, no data file, no upload. After the page has loaded it works with the network off.

    Frequently asked questions

    Is daylight saving taken into account?

    Yes, automatically. The offset is asked of the browser for the exact moment you are looking at, so a meeting planned across a change of clocks lands correctly on both sides.

    Why is the difference written as 5:30 and not 5 hours?

    Because India really is five and a half hours from London, and Nepal five and three quarters. Rounding those to whole hours would be wrong for a billion and a half people, so the minutes stay.

    Why is a city coloured green or grey?

    Green is the local working day, nine to six; grey is night. It is the answer to “can I call now” without doing any arithmetic in your head.

    Are my cities saved anywhere?

    They are remembered in your browser only, so the list is there when you come back. Nothing is sent anywhere — there is no account here to send it to.

    My city is not in the list. What now?

    Pick the one in the same zone — the time will be identical. The list is deliberately short so it stays usable: it covers the zones people actually compare, not all four hundred of them.

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